Update dependency phpseclib/phpseclib to ^3.0.57 [SECURITY]

[renovate]

ℹ️ Note

This PR body was truncated due to platform limits.

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
phpseclib/phpseclib (source)	^3.0.37 → ^3.0.57

---

phpseclib's AES-CBC unpadding susceptible to padding oracle timing attack

CVE-2026-32935 / GHSA-94g3-g5v7-q4jg

More information

Details

Impact

Those using AES in CBC mode may be susceptible to a padding oracle timing attack.

Patches

phpseclib/phpseclib@ccc21ae

Workarounds

Use AES in CTR, CFB or OFB modes

References

phpseclib/phpseclib@ccc21ae

Severity

• CVSS Score: 8.2 / 10 (High)
• Vector String: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

References

• https://github.com/phpseclib/phpseclib/security/advisories/GHSA-94g3-g5v7-q4jg
• https://github.com/phpseclib/phpseclib/commit/ccc21aef71eb170e9bf819b167e67d1fd9e6e788
• https://nvd.nist.gov/vuln/detail/CVE-2026-32935
• https://github.com/advisories/GHSA-94g3-g5v7-q4jg

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

---

phpseclib has a variable-time HMAC comparison in SSH2::get_binary_packet() using != instead of hash_equals()

CVE-2026-40194 / GHSA-r854-jrxh-36qx

More information

Details

phpseclib SSH2: Variable-time comparison in HMAC verification

Summary

phpseclib\Net\SSH2::get_binary_packet() uses PHP's != operator to compare a received SSH packet HMAC against the locally computed HMAC. != on equal-length binary strings in PHP uses memcmp(), which short-circuits on the first differing byte. This is a real variable-time comparison (CWE-208), proven by scaling benchmarks.

The finding is Low severity (defense-in-depth), not Critical. Practical exploitation over the network is prevented by SSH's disconnect-on-MAC-failure behavior combined with per-connection session keys. The fix is a one-liner: replace != with hash_equals(), which the codebase already uses in 9 other places.

• Target: phpseclib/phpseclib
• File: phpseclib/Net/SSH2.php
• Lines (master e819a163c): 3405 and 3410
• CWE: CWE-208 (Observable Timing Discrepancy)
• CVSS v3.1: 3.7 — CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
• Severity: Low (cryptographic hygiene / defense-in-depth)
• Affected branches: master, 3.0, 2.0, 1.0 (all supported versions)

Root cause

phpseclib/Net/SSH2.php lines 3399-3415 (master at e819a163c):

if ($this->hmac_check instanceof Hash) {
    $reconstructed = !$this->hmac_check_etm ?
        pack('Na*', $packet->packet_length, $packet->plain) :
        substr($packet->raw, 0, -$this->hmac_size);
    if (($this->hmac_check->getHash() & "\xFF\xFF\xFF\xFF") == 'umac') {
        $this->hmac_check->setNonce("\0\0\0\0" . pack('N', $this->get_seq_no));
        if ($hmac != $this->hmac_check->hash($reconstructed)) {                     // <-- line 3405
            $this->disconnect_helper(DisconnectReason::MAC_ERROR);
            throw new ConnectionClosedException('Invalid UMAC');
        }
    } else {
        if ($hmac != $this->hmac_check->hash(pack('Na*', $this->get_seq_no, $reconstructed))) {  // <-- line 3410
            $this->disconnect_helper(DisconnectReason::MAC_ERROR);
            throw new ConnectionClosedException('Invalid HMAC');
        }
    }
}

Both $hmac (read from the socket via Strings::pop($raw, $this->hmac_size) at line 3348) and the computed hash are equal-length binary strings. PHP's != operator on equal-length strings dispatches to zend_binary_strcmp() which internally calls memcmp(). Modern libc memcmp short-circuits on the first differing byte, producing a timing signal that scales linearly with the number of matching leading bytes.

The same bug exists on every supported branch

Branch	File	Line(s)	Expression
master (@​ e819a163c)	phpseclib/Net/SSH2.php	3405, 3410	$hmac != $this->hmac_check->hash(...)
3.0	phpseclib/Net/SSH2.php	3741, 3746	$hmac != $this->hmac_check->hash(...)
2.0	phpseclib/Net/SSH2.php	3796	$hmac != $this->hmac_check->hash(...)
1.0	phpseclib/Net/SSH2.php	3810	$hmac != $this->hmac_check->hash(...)

Verified with git show <branch>:phpseclib/Net/SSH2.php.

Reachability

The HMAC verification path at lines 3399-3415 is reached on every received SSH packet when the negotiated cipher is not AEAD — i.e., any of:

• aes128-cbc, aes192-cbc, aes256-cbc
• aes128-ctr, aes192-ctr, aes256-ctr
• 3des-cbc, 3des-ctr
• blowfish-cbc, blowfish-ctr
• twofish-*-cbc, twofish-*-ctr
• arcfour, arcfour128, arcfour256

combined with any non-AEAD MAC (hmac-sha2-256, hmac-sha2-512, hmac-sha1, hmac-sha1-96, hmac-md5, hmac-md5-96, umac-64, umac-128, and their -etm variants — full list at getSupportedMACAlgorithms() around line 4754).

AEAD ciphers (aes128-gcm@openssh.com, aes256-gcm@openssh.com, chacha20-poly1305@openssh.com) go through a different path (lines 3353-3381) and do not reach the != comparison — their authentication tag is checked inside the AEAD implementation.

$this->hmac_check is set during key exchange at SSH2.php:1812:

if (!$this->decrypt->usesNonce()) {
    [$this->hmac_check, $checkKeyLength] = self::mac_algorithm_to_hash_instance($mac_algorithm_in);
    $this->hmac_size = $this->hmac_check->getLengthInBytes();
}

So any SSH2 client session negotiating a non-AEAD cipher exercises the vulnerable code path starting from the first post-KEX packet.

Contrast with existing code that does the right thing

hash_equals() is already used in 9 other places in the phpseclib codebase, proving the maintainer knows the pattern:

phpseclib/File/CMS/DigestedData.php:186
phpseclib/File/CMS/SignedData/Signer.php:294
phpseclib/File/CMS/SignedData/Signer.php:406
phpseclib/Crypt/Common/Formats/Keys/PuTTY.php:236
phpseclib/Crypt/RSA/PublicKey.php:98, 105, 188, 229
phpseclib/Crypt/RSA/PrivateKey.php:386

The SSH2 MAC comparison is the one place it was missed.

Proof of concept

All scripts under poc/. They prove three things:

1. PHP's != on equal-length binary strings IS variable-time and short-circuits.
2. hash_equals() is constant-time over the same inputs.
3. Applied to 32-byte HMAC-SHA256 values as produced by phpseclib's Crypt\Hash class, the code path at SSH2.php:3405/3410 leaks ~2-14 ns of signal per comparison.

PoC 1: baseline measurement (poc/01_verify_variable_time.php)

Measures != vs hash_equals() on 32-byte strings with first-byte vs last-byte mismatch. 500,000 iterations each, trimmed mean, Welch's t-test.

Representative output (PHP 8.3.6 on Linux x86_64):

=== PHP != operator vs hash_equals() on 32-byte strings ===
Iterations: 500000

!= first-byte mismatch: median=40 p25=40 p75=50 tmean=44.3
!= last-byte mismatch:  median=50 p25=40 p75=50 tmean=46.4
Gap (last - first):     tmean_delta=2.1 ns

hash_equals first-byte: median=110 tmean=112.7
hash_equals last-byte:  median=111 tmean=114.9
Gap (last - first):     tmean_delta=2.2 ns

The 32-byte delta is small (~2 ns) and lives in the noise. This alone doesn't prove variable-time behavior. PoC 2 does.

PoC 2: scaling test (poc/02_scaling_test.php)

The decisive test. If != is truly constant-time, timing should not depend on mismatch position. If it short-circuits, timing should scale linearly with prefix length. Test strings from 32 bytes to 4096 bytes.

Length  32 bytes: range (first-last byte mismatch) =   1.72 ns
Length  64 bytes: range                            =   2.42 ns
Length 128 bytes: range                            =   8.33 ns
Length 256 bytes: range                            =  16.91 ns
Length 512 bytes: range                            =  38.89 ns
Length 1024 bytes: range                           =  81.16 ns
Length 4096 bytes: range                           = 284.26 ns

This is monotone, linear scaling. Confirmed variable-time: != short-circuits. Per-byte delta ≈ 0.089 ns/byte (4096 bytes → ~284 ns → 284/4096 ≈ 0.069 ns/byte after accounting for the fixed call overhead).

PoC 3: contrast with hash_equals() (poc/03_hash_equals_scaling.php)

Same test, != vs hash_equals() on 1024-byte strings:

Mismatch pos         | != tmean (ns)        | hash_equals tmean
----------------------------------------------------------------------
byte    0            |    83.72 (sd  4.79) |   873.78 (sd 100.71)
byte  128            |    98.48 (sd  8.27) |   855.10 (sd 87.50)
byte  256            |   103.36 (sd  7.01) |   869.21 (sd 89.61)
byte  512            |   125.65 (sd 10.07) |   879.74 (sd 81.82)
byte  768            |   145.73 (sd  9.96) |   848.59 (sd 84.34)
byte 1023            |   175.33 (sd 14.31) |   852.24 (sd 85.81)

!= range (last - first):          91.62 ns
hash_equals range (last - first): 31.15 ns

!= monotonically increases with mismatch position. hash_equals is flat; the 31 ns range is measurement jitter (sd ≈ 90 ns > range).

Per-byte delta from this run: 91.62 / 1023 ≈ 0.089 ns/byte. Extrapolated to 32-byte HMAC: ~2.86 ns total signal between first-byte-diff and last-byte-diff.

PoC 4: end-to-end with phpseclib's Hash class (poc/04_phpseclib_in_context.php)

Uses phpseclib4\Crypt\Hash (the exact class bound to $this->hmac_check) to compute a real HMAC-SHA-256, then executes the exact expression $hmac != $this->hmac_check->hash(...) from SSH2.php:3410:

Using != (SSH2.php:3405,3410 pattern):
  first-byte mismatch: 44.33 ns
  last-byte mismatch:  58.19 ns
  Δ (last - first):    13.86 ns  <-- timing leak signal

Using hash_equals() (the fix):
  first-byte mismatch: 113.67 ns
  last-byte mismatch:  112.93 ns
  Δ (last - first):    -0.74 ns  <-- should be flat (noise)

The 13.86 ns vs 2.86 ns variation between runs is within measurement variance — the signal is real and the sign matches every run (last > first for !=, flat for hash_equals).

Impact

Severity: Low (defense-in-depth). This is a real CWE-208 instance, but it is not a practical remote vulnerability.

Why exploitation over the network is infeasible

1. Signal is tiny. ~3-14 ns per HMAC compare. Network RTT jitter on a reasonable LAN is 100 µs (100,000 ns). On the internet it is 1-10 ms. The signal-to-noise ratio for a remote observer is ~1e-5 to 1e-7.

2. One measurement per connection. On every MAC failure, SSH2.php:3406/3411 calls disconnect_helper(MAC_ERROR) and throws. The connection is torn down. A reconnect goes through a fresh key exchange, producing a new HMAC key. The HMAC over a fresh key is uncorrelated with the prior HMAC. An attacker cannot accumulate prefix-matching information across connections because there is no fixed target.

3. MAC is over sequence-numbered data. Each packet's MAC input includes $this->get_seq_no (line 3410) or a nonce (line 3404). Even within a single connection, replays are impossible — every MAC is bound to a distinct seq number. There is no stable oracle to probe.

4. No adaptive probe. A Bleichenbacher/Lucky13-style attack needs tens of thousands of adaptive queries against a single secret. SSH's hard disconnect eliminates this primitive entirely.

5. Rough sample-count requirement. To distinguish a 3 ns signal from 1 ms jitter with high confidence you need roughly (noise / signal)^2 ≈ (1e6 / 3)^2 ≈ 1e11 independent samples. With one sample per connection (and each connection being against a fresh secret), this is unreachable on any practical scale.

What remains real

1. Cryptographic hygiene. A security library should not use non-constant-time comparison on MACs, period. That is standard practice (RFC 4634, NIST SP 800-131A guidance on cryptographic implementations).
2. Code correctness / API consistency. The library already uses hash_equals() in 9 other comparable places. The SSH2 MAC path is inconsistent with the rest of the codebase.
3. Future-proofing. If PHP or the underlying memcmp() implementation changes, or if a future MAC algorithm uses longer digests, the signal grows linearly. A constant-time comparison eliminates the concern permanently.
4. Static analysis / audit hygiene. Cryptographic linters (e.g., GitHub CodeQL's js/timing-attack, phpcs-security-audit) flag non-constant-time comparisons on secret values. A clean codebase passes those checks.

CVSS breakdown

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N = 3.7 (Low)

• AV:N — network path, attacker on the SSH transport.
• AC:H — extremely high complexity; remote exploitation is not demonstrated and is believed infeasible.
• PR:N/UI:N — no prior auth or interaction needed to observe the timing (if there were any signal).
• S:U — no scope change.
• C:L / I:N / A:N — theoretical information exposure of MAC prefix bits only, no integrity or availability impact.

This is the same vector string used for CVE-2026-32935 (the recent AES-CBC padding oracle in the same library), differing only in Confidentiality (L vs H) because padding oracle actually recovers plaintext whereas this MAC timing does not enable any known plaintext recovery.

Fix

Two-line patch:

--- a/phpseclib/Net/SSH2.php
+++ b/phpseclib/Net/SSH2.php
@@ -3402,12 +3402,12 @@ class SSH2
                 substr($packet->raw, 0, -$this->hmac_size);
             if (($this->hmac_check->getHash() & "\xFF\xFF\xFF\xFF") == 'umac') {
                 $this->hmac_check->setNonce("\0\0\0\0" . pack('N', $this->get_seq_no));
-                if ($hmac != $this->hmac_check->hash($reconstructed)) {
+                if (!hash_equals($this->hmac_check->hash($reconstructed), $hmac)) {
                     $this->disconnect_helper(DisconnectReason::MAC_ERROR);
                     throw new ConnectionClosedException('Invalid UMAC');
                 }
             } else {
-                if ($hmac != $this->hmac_check->hash(pack('Na*', $this->get_seq_no, $reconstructed))) {
+                if (!hash_equals($this->hmac_check->hash(pack('Na*', $this->get_seq_no, $reconstructed)), $hmac)) {
                     $this->disconnect_helper(DisconnectReason::MAC_ERROR);
                     throw new ConnectionClosedException('Invalid HMAC');
                 }

The same one-liner should be applied to phpseclib/Net/SSH2.php on 3.0 (lines 3741, 3746), 2.0 (line 3796), and 1.0 (line 3810).

hash_equals() is a built-in PHP function available since PHP 5.6. phpseclib's minimum PHP version for all supported branches is well above that, so there is no compatibility concern — and indeed, as noted, hash_equals() is already used throughout the codebase for exactly this purpose.

PoC 5: prefix-position byte-recovery test (poc/05_prefix_position_test.php)

The critical question: can an attacker recover the MAC byte-by-byte? Tests candidate MACs with 0, 1, 2, ..., 31 correct leading bytes using phpseclib's Crypt\Hash class. 500,000 iterations per position.

 0 correct prefix bytes: tmean= 65.75 ns  sd= 4.89 ns
 1 correct prefix bytes: tmean= 66.36 ns  sd= 4.77 ns
 2 correct prefix bytes: tmean= 60.06 ns  sd= 5.29 ns
 4 correct prefix bytes: tmean= 58.08 ns  sd= 5.24 ns
 8 correct prefix bytes: tmean= 66.93 ns  sd= 4.60 ns
12 correct prefix bytes: tmean= 64.01 ns  sd= 4.83 ns
16 correct prefix bytes: tmean= 61.81 ns  sd= 5.55 ns
20 correct prefix bytes: tmean= 60.46 ns  sd= 5.40 ns
24 correct prefix bytes: tmean= 60.53 ns  sd= 4.06 ns
28 correct prefix bytes: tmean= 60.54 ns  sd= 3.99 ns
31 correct prefix bytes: tmean= 59.04 ns  sd= 3.96 ns

Range (0 prefix vs 31 prefix): -6.71 ns (NEGATIVE)

No monotonic signal. The range is negative (wrong direction for an oracle), and the standard deviations (4-5 ns) are larger than any observed position-dependent delta. Byte-by-byte MAC recovery is not feasible even locally on 32-byte HMACs.

This conclusively rules out the "timing oracle for MAC forgery" escalation path.

Escalation angles investigated and ruled out

9 rounds of external review suggested various escalation paths. Every one is dead:

Angle	Result	Evidence
Byte-by-byte MAC recovery	Dead	PoC 5: no monotonic signal at 32 bytes (-6.71ns range, wrong sign)
Persistent oracle (connection survives MAC failure)	Dead	disconnect_helper() + throw is unconditional (3406-3412); reset_connection() clears all state
Sequence desync (Terrapin-style)	Dead	get_seq_no++ at 3469 is AFTER MAC check; failed MAC throws before increment
SSH_MSG_IGNORE MAC bypass	Dead	All message types go through get_binary_packet() MAC check before filter()
Memory exhaustion via packet_length	Dead	packet_length capped at 0x9000 (36KB) at line 3542
State machine abuse / fail-open	Dead	reset_connection() nulls socket, clears bitmap, all crypto state
Protocol downgrade on MAC failure	Dead	Immediate disconnect, no fallback or renegotiation
Padding oracle chain (Lucky13)	Dead	MAC check (3405) is BEFORE padding interpretation (3418)
SFTP subsystem bypass	Dead	SFTP uses same SSH2 transport, same MAC verification
BigInteger type confusion	Dead	Engine selected at construction, not per-packet
Pre-auth reachability	Yes, but irrelevant	One guess per connection with fresh keys = no oracle

Devil's advocate review

Every objection I could think of, addressed:

"This is just a code smell. Show me a real exploit."
Acknowledged. The report does not claim remote exploitability. It is submitted as Low / defense-in-depth, consistent with how similar findings are treated in other cryptographic libraries (see e.g. OpenSSH commits replacing memcmp() with timingsafe_bcmp for similar reasons).

"PHP's != might not even short-circuit — you're just seeing noise."
PoC 2 rules this out. Timing scales monotonically and nearly linearly with mismatch position across a 128x range of string lengths (32 bytes → 4096 bytes). That is not noise.

"SSH disconnects on MAC failure, so you only get one sample. Case closed."
Correct, and the report says so explicitly. This is why the severity is Low rather than High.

"There is no adaptive probe because session keys rotate per connection."
Correct, and the report says so explicitly. This is the primary reason the network attack is infeasible.

"Is this Lucky13-style? Does the MAC check happen after padding?"
No. MAC verification at SSH2.php:3399-3414 runs BEFORE any padding interpretation. Padding length is only read at line 3418, strictly after the MAC check. There is no unpadding oracle here. (Lucky13 in phpseclib's AES-CBC decrypt path is a separate, already-fixed issue — CVE-2026-32935.)

"Maybe the get_seq_no or nonce path somehow enables forgery."
No. The seq number is deterministic (incremented by one per packet) and the nonce (for UMAC) is derived from it. Neither is attacker-controlled in any useful sense. The MAC key is the secret, and it is per-connection.

"Is this already reported?"
Searched published advisories (gh api repos/phpseclib/phpseclib/security-advisories). Only CVE-2026-32935 is published, for a different code path (AES-CBC padding oracle after MAC verification). The SSH2 MAC comparison issue is not covered by any published advisory. The fix commit for CVE-2026-32935 (ccc21aef71eb170e9bf819b167e67d1fd9e6e788) did not touch SSH2.php:3405 or :3410.

"Does the project's threat model even consider this in scope?"
SECURITY.md says "To report a security vulnerability, please use the Tidelift security contact." It does not exclude timing side-channels. The maintainer has already fixed constant-time comparison issues in other parts of the library (RSA, OAEP, AES-CBC padding) and uses hash_equals() in 9 other places. This issue is consistent with the maintainer's existing security posture, and the fix is trivial.

"Is the Low severity appropriate? Could it be informational?"
Low is appropriate. "Informational" would be for something that is provably no-impact. This is a demonstrable CWE-208 instance on secret-dependent data. It scores 3.7 under CVSS v3.1 with AC:H and C:L. That is Low, not Informational. The recent CVE-2026-32935 is assigned for a timing-side-channel in the same file category and given CVSS 4.0 = 8.2 (their vector is more severe because padding oracle actually recovers plaintext). This one would score lower than that, which matches the Low designation.

"Would a maintainer just close this?"
Unlikely. The fix is a one-liner, there is no behavioral change, it aligns with existing code style in the same codebase, and it silences future audit findings. The maintainer has a track record of accepting similar hardening patches. If they close it, the reason would likely be "we already know, not worth a CVE" — which would still leave the code fixed, which is the goal.

Suggested reporting path

GitHub PVR is enabled for phpseclib/phpseclib ({"enabled":true}). SECURITY.md says to use the Tidelift contact, but GitHub PVR is a reasonable alternative and lets the maintainer decide whether to coordinate with Tidelift. Either path is acceptable.

Given the Low severity, this could also be filed as a public pull request rather than a security advisory. That would be faster for everyone and avoids using the private disclosure channel for a hardening fix.

Files

• poc/01_verify_variable_time.php — baseline 32-byte timing measurement
• poc/02_scaling_test.php — decisive scaling test across string lengths
• poc/03_hash_equals_scaling.php — != vs hash_equals() comparison
• poc/04_phpseclib_in_context.php — end-to-end repro using phpseclib's Crypt\Hash
• notes.md — research notes, dead ends, escalation angles considered
• prior-work.md — prior work search results
• status.json — machine-readable status

Koda Reef

Severity

• CVSS Score: 3.7 / 10 (Low)
• Vector String: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

References

• https://github.com/phpseclib/phpseclib/security/advisories/GHSA-r854-jrxh-36qx
• https://github.com/phpseclib/phpseclib/commit/ffe48b6b1b1af6963327f0a5330e3aa004a194ac
• https://github.com/phpseclib/phpseclib/releases/tag/1.0.28
• https://github.com/phpseclib/phpseclib/releases/tag/2.0.53
• https://github.com/phpseclib/phpseclib/releases/tag/3.0.51
• https://nvd.nist.gov/vuln/detail/CVE-2026-40194
• https://github.com/advisories/GHSA-r854-jrxh-36qx

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

---

phpseclib has a CVE-2024-27355 mitigation bypass — OID amplification DoS in ASN1::decodeOID()

CVE-2026-44167 / GHSA-3qpq-r242-jqj7

More information

Details

Impact

Anyone loading untrusted ASN1 files (eg. X509 certificates, RSA PKCS8 private or public keys, etc)

Patches

phpseclib/phpseclib@d53d202

Workarounds

No.

References

phpseclib/phpseclib@d53d202

Severity

• CVSS Score: 7.5 / 10 (High)
• Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

• https://github.com/phpseclib/phpseclib/security/advisories/GHSA-3qpq-r242-jqj7
• https://github.com/phpseclib/phpseclib/commit/d53d2021bcb9f6a04d5d44ec99e6bbef219a71bc
• https://nvd.nist.gov/vuln/detail/CVE-2026-44167
• https://github.com/advisories/GHSA-3qpq-r242-jqj7

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

---

phpseclib: X.509 certificate validation sends attacker-controlled outbound requests (server-side request forgery) via Authority Information Access

CVE-2026-55599 / GHSA-m557-wrgg-6rp4

More information

Details

Summary

When an application validates an untrusted X.509 certificate with phpseclib, X509::validateSignature() reads a URL out of that certificate's Authority Information Access (AIA) extension and connects to it. Attacker who supplies certificate fully controls host, port, and path of that connection. URL fetching is enabled by default, and no destination is blocked. An unauthenticated attacker can therefore make a validating server open connections to internal hosts and ports it should never reach, for example loopback 127.0.0.1, cloud metadata address 169.254.169.254, and internal-only services. This is a server-side request forgery (SSRF) caused by an insecure default. It is reproducible on current released LTS 3.0.53 and on 4.0 development line.

Details

When no already-trusted certificate authority is the issuer of certificate under validation, validateSignatureCountable() continues to AIA fetching. Default for validateSignature() is caonly = true:

// phpseclib/File/X509.php:1316-1327 (4.0 development line, commit 74ada1a6)
if (!isset($signingCert)) {
    if ($caonly) {
        return $this->testForIntermediate(true, $count) && $this->validateSignature(true);
    } else {
        try {
            $this->testForSelfSigned();
            $signingCert = $this;
        } catch (BadMethodCallException) {
            return $this->testForIntermediate(true, $count) && $this->validateSignature(true);
        }
    }
}

testForIntermediate() takes URL straight out of certificate's AIA caIssuers field and fetches it. Value comes directly from certificate content and is never restricted:

// phpseclib/File/X509.php:1357-1391 (4.0 development line)
$opts = $this->getExtension('id-pe-authorityInfoAccess');
...
foreach ($opts['extnValue'] as $opt) {
    if ($opt['accessMethod'] == 'id-ad-caIssuers') {
        if (isset($opt['accessLocation']['uniformResourceIdentifier'])) {
            $url = (string) $opt['accessLocation']['uniformResourceIdentifier']; // attacker controlled
            break;
        }
    }
}
...
$cert = static::fetchURL($url); // server-side request forgery

fetchURL() connects to attacker host and port. There is no destination validation: no block on loopback, link-local, private, or metadata ranges, and no port restriction:

// phpseclib/File/X509.php:1456-1476 (4.0 development line)
private static function fetchURL(string $url): ?string
{
    if (self::$disable_url_fetch) {  // default false, so fetching happens
        return null;
    }
    $parts = parse_url($url);
    switch ($parts['scheme']) {
        case 'http':
            $fsock = @fsockopen($parts['host'], $parts['port'] ?? 80); // attacker host and port
            ...
            fputs($fsock, "GET $path HTTP/1.0\r\n");
            fputs($fsock, "Host: $parts[host]\r\n\r\n");

Fetching is on by default:

// phpseclib/File/X509.php:110 (4.0 development line)
private static bool $disable_url_fetch = false;

Same default-enabled logic exists in released 3.0.x. In 3.0.53 it sits at $disable_url_fetch = false on line 255 and fsockopen($parts['host'], ...) on line 1136 of phpseclib/File/X509.php.

Why this is a vulnerability and not merely a feature. AIA chasing is a legitimate capability described by RFC 4325, and this report does not claim fetching is wrong in itself. Vulnerability is the combination of three properties that together match definition of SSRF:

1. URL comes from untrusted input. It is read out of certificate that an application is trying to validate, which is exactly the data an attacker controls.
2. Fetching is enabled by default. An integrator who simply calls validateSignature() gets outbound requests with no opt-in. Only control, X509::disableURLFetch(), is off by default, so secure behaviour requires knowing about and calling a method that most callers never see.
3. No destination is restricted. Loopback, private ranges, link-local metadata, and arbitrary ports are all reachable. Mature implementations of AIA fetching restrict destinations precisely to prevent this.

Reachability is not narrow. Fetch triggers whenever certificate's issuer is not already trusted, which an attacker arranges trivially by choosing any issuer name that is not in trust store. Having certificate authorities loaded does not protect a target: an attacker certificate that claims an unknown issuer still reaches testForIntermediate().

Response handling is blind. Fetched body is used only if it parses as a certificate, and is otherwise discarded, so an attacker does not directly read internal responses through this path. That limits confidentiality impact but does not remove request-forgery and reconnaissance capability.

PoC

Two reproductions follow: current released LTS 3.0.53, and 4.0 development line. Malicious certificate is plain PEM and is identical for both, since certificate format is the same across versions.

Build malicious certificate once (this uses 4.0 to build, but any tool that emits an X.509 certificate with an AIA caIssuers URL works):

composer require phpseclib/phpseclib:4.0.x-dev

<?php
require 'vendor/autoload.php';

use phpseclib4\Crypt\RSA;
use phpseclib4\File\X509;

$url = 'http://127.0.0.1:19090/ssrf';

$key  = RSA::createKey(2048)->withPadding(RSA::SIGNATURE_PKCS1)->withHash('sha256');
$cert = new X509($key->getPublicKey());
$cert->addDNProp('id-at-commonName', 'attacker-leaf.example');
$cert->setEndDate('lifetime');
$cert->setExtension('id-pe-authorityInfoAccess', [
    ['accessMethod' => 'id-ad-caIssuers',
     'accessLocation' => ['uniformResourceIdentifier' => $url]],
]);
$key->sign($cert);
file_put_contents('attacker_cert.pem', (string) $cert);

Stand up a listener that represents an internal service on a port that is not otherwise reachable from outside:

php -r '$s=stream_socket_server("tcp://127.0.0.1:19090",$e,$m);$c=stream_socket_accept($s,20);echo fread($c,4096);'

Reproduction on released LTS 3.0.53. Install it and have an application validate certificate:

composer require phpseclib/phpseclib:~3.0.0

<?php
require 'vendor/autoload.php';

use phpseclib3\File\X509;

$v = new X509();
$v->loadX509(file_get_contents('attacker_cert.pem'));
$v->validateSignature();   // connects to 127.0.0.1:19090 during validation

Reproduction on 4.0 development line. Same certificate, 4.0 namespace:

<?php
require 'vendor/autoload.php';

use phpseclib4\File\X509;

X509::clearCAStore();      // attacker cert issuer is not trusted
$v = X509::load(file_get_contents('attacker_cert.pem'));
$v->validateSignature();   // connects to 127.0.0.1:19090 during validation

Observed result, on both 3.0.53 and 4.0.x-dev. Listener receives a request whose host, port, and path all come from certificate, even though validateSignature() returns false:

GET /ssrf HTTP/1.0
Host: 127.0.0.1

This was also confirmed end to end over HTTP: an unauthenticated POST of certificate to an endpoint that calls loadX509() then validateSignature() makes server connect outbound to attacker-chosen 127.0.0.1:19090. Changing host and port in certificate reaches any internal address and port, for example 169.254.169.254 or 127.0.0.1:6379.

Negative control. With X509::disableURLFetch() set before validation, validation returns false and no outbound connection is made. This confirms both root cause and that default-on behaviour is the trigger.

Impact

This is a server-side request forgery (CWE-918) caused by an insecure default (CWE-276): URL fetching is enabled by default and applies no destination restrictions while acting on untrusted certificate content.

An application is affected when it validates an attacker-influenced certificate, which covers client-certificate checks implemented in PHP, S/MIME and CMS signer verification, document and code-signing validation, and any feature that verifies an uploaded or pasted certificate. No authentication and no user interaction are needed.

What an attacker gains:

• Internal reconnaissance and port scanning. Connection success or failure and timing reveal which internal hosts and ports respond.
• Interaction with internal-only HTTP services such as admin panels, dashboards, and webhooks bound to loopback or private ranges.
• Requests to cloud metadata endpoints such as 169.254.169.254, which answer plain HTTP GET on some providers.

Because fetch is blind, an attacker does not read internal response bodies through this path directly, so this is a request-forgery and reconnaissance primitive rather than direct disclosure of internal data. Any reflective sink elsewhere in an application, or any internal endpoint that performs an action on a GET, increases real impact.

Suggested fix, strongest first: default disableURLFetch to true so AIA chasing is opt-in; if it stays enabled, validate destinations inside fetchURL() by rejecting loopback, link-local, and private addresses and restricting ports, and add an egress policy callback similar to existing setCRLLookupCallback(); and state plainly in documentation that validating an untrusted certificate can cause outbound requests to URLs found inside that certificate.

Severity

• CVSS Score: 5.8 / 10 (Medium)
• Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N

References

• https://github.com/phpseclib/phpseclib/security/advisories/GHSA-m557-wrgg-6rp4
• https://nvd.nist.gov/vuln/detail/CVE-2026-55599
• https://github.com/advisories/GHSA-m557-wrgg-6rp4

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

---

phpseclib — non-constant-time X25519 scalar multiplication permits full private-key recovery

CVE-2026-84308 / GHSA-q97c-8qh3-fpc6

More information

Details

The pure-PHP X25519 scalar multiplication in phpseclib is not constant-time. Field addition and subtraction each perform a data-dependent conditional modular reduction, so the cost of each Montgomery-ladder step is a linear function of that step's reduction count which is a quantity determined by the secret scalar's prefix.

An observer with per-ladder-step resolution recovers the 251-bit clamped private scalar. This is a per-step leak, not an aggregate one: an instrumented code proof-of-concept recovers 20/20 test keys from 32 observed operations, and an observer that counts libgmp calls instead of timing them recovers a key from a single operation.

This is not a low-order-input issue. Recovery works with the RFC 7748 base point u = 9, with no attacker-chosen input at all. Rejecting low-order public values does not close it.

2. Affected component

Confirmed on phpseclib 3.0.56 (338 files under phpseclib/,sha256(sorted(relpath NUL file_sha256 LF)) = cc7250b611f520e809131aab0931503457c44d8cbfb10d535251c6fec5f62a2b).
The code appears unchanged across the 3.0 series wherever Curve25519 is supported, please confirm the affected range.

file:line	role
Math/PrimeField/Integer.php:189	add() — conditional subtract($modulo) when the sum ≥ p
Math/PrimeField/Integer.php:207	subtract() — conditional add($modulo) when the result is negative
Crypt/EC/BaseCurves/Montgomery.php:229–234	ladder branch on the secret bit, selecting argument order of doubleAndAddPoint
Crypt/EC/Formats/Keys/MontgomeryPrivate.php:66	multiplyPoint(getBasePoint(), dA) — no engine check of any kind
Crypt/EC/Formats/Keys/PKCS8.php:194–200	the same derivation, correctly gated on ext-sodium — the pattern MontgomeryPrivate is missing

3. Technical description

Operation counts in the ladder are already constant — 10 field multiplications, 4 additions and 4 subtractions per step, 2560 multiplications per 256-step ladder. Operand values are not. Each PrimeField\Integer::add() / subtract() takes a data-dependent branch costing ~0.85–1.0 µs on the GMP engine, against a ~32 µs step period, so per-step cost is α + β·c where c is that step's conditional-reduction count. Measured across 20 keys: R² = 0.91–0.98, β = 838–920 ns.

c depends on the whole scalar prefix, not on the current bit, so per-step thresholding is useless — it saturates at ~93% per bit for u = p−1 and at chance for u = 9, and recovers 0/20 keys either way, because the bit string is a prefix-XOR in which one flipped step inverts the entire tail. Conditioning on the prefix removes the ambiguity: a beam search replays both branches from each candidate ladder state, reads off the exact c for each, and scores against the observation. The victim's public key adjudicates the small residual search.

Two facts bound the problem and are worth stating precisely, because they determine whether a fix is needed at all:

• Aggregate observation is provably useless. The adjacent-bit transition count T(k) has exact entropy H(T) = 4.0357 bits over clamped scalars, so a noiseless transition-count oracle still leaves ~2^247 candidates. The summed reduction count Σc is richer (~6.6–6.9 bits) and still leaves ~2^244. Any measurement that collapses the call to one number is safe. Per-step measurement is not.
• The libgmp call counts are exactly determined. Per ladder step, __gmpz_add = 4 + csub, __gmpz_sub = 4 + cadd, __gmpz_mul = __gmpz_mod = 10. Verified by differencing gdb breakpoint counts against phpseclib's own doubleAndAddPoint — 27/27 steps exact, extended independently to 64/64 and 38/38 by our two reviewers. An observer that only counts these calls needs no timing, no calibration and no repetition.

Results, 20 keys × 3 sampling seeds, 800 traces per path collected from 800 distinct PHP processes (so the observations are cross-process, as real requests would be):

observer	path	observations needed	exact 251-bit recovery
timing	key load, u = 9	32	20/20 keys, 95% CI [83.9%, 100%]
timing	ECDH, u = p−1	32	18/20 keys, 95% CI [69.9%, 96.8%]
timing	either	8	18–23% of trials
libgmp call counts	either	1	20/20 keys; tolerates 20–30% of per-step counts being wrong

The model underlying the decoder is validated against the pinned implementation: 254/254 (key, peer) outputs match the real DH::computeSecret, and all four RFC 7748 §6.1 vectors match both phpseclib and the published constants.

Negative controls are clean — wrong public key, shuffled trace, wrong peer value, foreign key: 0/20 in every case. Nothing derived from the private key reaches the decoder; its inputs are the observation vector, the peer value, the victim's public key, and the public clamping constants.

5. Impact

In the instrumented, local model, recovery of the clamped scalar gives a permanent compromise of the X25519 private key. Clamping is applied on every call, so the recovered value is what every past and future operation with that key uses.

6. Restrictions

Required for exploitation:

1. A reused / long-lived X25519 private key. Ephemeral X25519 — the normal TLS and SSH case — defeats this outright. phpseclib's own SSH path generates a fresh scalar per exchange and is not affected.
2. Knowledge of the victim's public key. It adjudicates the decoder's residual search; without it no candidate can be selected. This is normally public, but it is a precondition, not a convenience.
3. The pure-PHP path must actually run. Measured across four extension configurations:
   • EC::loadFormat('MontgomeryPrivate', $raw32) runs the ladder in every
     configuration — but the format declares IS_INVISIBLE (MontgomeryPrivate.php:40),
     so PublicKeyLoader::load skips it and nothing inside phpseclib calls it. An
     application must name the format explicitly.
   • PKCS8 / PublicKeyLoader::load / EC::createKey run the ladder only when ext-sodium is absent — PKCS8.php:194 gates on sodium_crypto_box_publickey_from_secretkey. OpenSSL does not help here.
   • DH::computeSecret runs the ladder only under EC::forceEngine('PHP'), or when both openssl_pkey_derive (DH.php:325) and sodium_crypto_scalarmult (EC/PrivateKey.php:75) are unavailable. ext-sodium is bundled and enabled by default in PHP 7.2+, so the reachable configurations are a minority — though disable_functions hardening and --disable-sodium builds do occur, particularly in shared hosting.
4. An observer with per-ladder-step resolution, i.e. one that can distinguish ~0.9 µs within a ~32 µs step, or count libgmp entry-point calls. In practice that means local co-residency (e.g. a Flush+Reload spy on the shared libgmp.so mapping — __gmpz_add / __gmpz_sub are the correct targets; __gmpn_* are not, being size-dispatched internals).

Not demonstrated — stated so it is not found rather than disclosed:

• We did not build a co-resident spy. Per-step observations in the PoC come from a small hrtime() hook inside Montgomery::multiplyPoint (one file differs from the pinned tree; Math/PrimeField/Integer.php, which carries the leak, is byte-identical). This models an observer with intra-call resolution; it is not itself an attacker capability. We note that the requisite primitives are present on ordinary hardware — on our test host clflush and rdtscp work, with 187–312 cycle cached/flushed separation — but building and validating a spy is separate work we have not done.
• Perfect step segmentation is assumed. A real observer must recover step boundaries and separate the ladder from the surrounding modular inversion.
• A single host and configuration. All timing figures are from one 2-vCPU shared VM (PHP 8.3.6, GMP 6.3.0). A noisier host needs more observations; recovery holds within roughly 25–30% additional noise beyond this host's residual.
• We have not identified an affected deployed caller.

Accordingly we report this as a hardening issue and demonstrated side channel, not as a completed remote exploit.

8. Suggested remediation

1. Constant-time, fixed-width field arithmetic, or delegate to a vetted native provider. This is the actual fix. Removing the ladder's bit branch is not sufficient while Integer.php:189 and :207 remain operand-dependent.
2. Gate MontgomeryPrivate.php:66 the way PKCS8.php:194–200 already is. That is a one-block change and it closes the only entry point that is un-gated in every configuration. Keep the $curve instanceof Curve25519 guard — MontgomeryPrivate also accepts Curve448 keys.
3. Consider an OpenSSL arm alongside the sodium arm in PKCS8::loadECDH, or fail closed, so stacks without ext-sodium do not fall through to the ladder.
4. Separately, and unrelated to this channel: the pure-PHP path returns an all-zero 32-byte shared secret for low-order peer inputs. Rejecting the full canonicalised low-order set and adding a constant-time all-zero check is correct hygiene for contributory behaviour — but it does not mitigate the timing channel, since recovery works with u = 9.

Contact

George Stergiopoulos
Assistant Professor of cybersecurity
Athens University of Economics and Business, Greece
E: geostergiop@aueb.gr | s: https://www.aueb.gr/en/faculty_page/stergiopoulos-georgios

Severity

• CVSS Score: 6.3 / 10 (Medium)
• Vector String: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

References

• https://github.com/phpseclib/phpseclib/security/advisories/GHSA-q97c-8qh3-fpc6
• https://nvd.nist.gov/vuln/detail/CVE-2026-84308
• https://github.com/phpseclib/phpseclib/commit/fb56bc5bb9009b54a6c26b31aeec8ed944f17373
• https://github.com/phpseclib/phpseclib/releases/tag/3.0.57
• https://github.com/phpseclib/phpseclib/releases/tag/4.0.1
• https://github.com/advisories/GHSA-q97c-8qh3-fpc6

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

---

Release Notes

phpseclib/phpseclib (phpseclib/phpseclib)

v3.0.57

Compare Source

• ASN1: fix tag matching for tagged CHOICE children (#​2158)
• RSA: fix for openssl_verify calls that error out (#​2161)
• RSA/PublicKey: implement salt length discovery for PSS verification (#​2164)
• BigInteger/PHP: don't return the divisor as the common residue (#​2165)
• Curve25519/448: improve timing attack resistance (CVE-2026-84308)

v3.0.56

Compare Source

• RSA: don't use OpenSSL for PSS on OpenSSL < 3.1.0 (#​2152)
• SFTP: throw TimeoutExceptions on timeout vs UnexpectedValueException (#​2156)
• SFTP/Stream: use default context if one isn't explicitly provided (#​2154)

v3.0.55

Compare Source

• RSA: signature verification with PKCS1 with failed when the parameters field was absent

v3.0.54

Compare Source

• X509: add setURLFetchCallback() method (CVE-2026-55599)

v3.0.53

Compare Source

• RSA: decryption with password protected keys didn't work with OpenSSL engine (#​2140)
• ASN1: speed up OID calculations
• SFTP: add hardlink() method (#​2142)
• DES: fix PHP deprecations (#​2145)

v3.0.52

Compare Source

• ASN1: more stringent OID length limits (CVE-2026-44167)
• RSA: OpenSSL 3.2+ changed how PKCS1 decryption works (#​2136)
• Keys/OpenSSH: support comments with spaces in them (#​2137)

v3.0.51

Compare Source

• SSH2: use constant time string comparison in get_binary_packet() (CVE-2026-40194)
• RSA: add sha3 support (#​2132)
• use new OpenSSL functionality (#​2130)

v3.0.50

Compare Source

• fix for PHP 8.5 BC breaking changes on 32-bit machines (#​2126)
• make unpadding in CBC mode constant time (CVE-2026-32935)
• X509: add support for organizationIdentifier (#​2128)

v3.0.49

Compare Source

• more PHP 8.5 deprecations (#​2113)
• Keys/OpenSSH: add support for pub keys with multiple spaces / tabs (#​2116)

v3.0.48

Compare Source

• readd SCP support (#​2108)
• SSH2: adjust want_reply handling for GLOBAL_REQUEST and CHANNEL_REQUEST (#​2111)
• ASN1: add more validation checks to asn1map (#​2104)
• RSA/PSS: more elegant int conversion (#​2107)
• more PHP 8.5 deprecations (#​2103, #​2113)

v3.0.47

Compare Source

• fix PHP 8.5 deprecations
• SFTP: check if realpath succeeded when changing SFTP directory (#​2098)
• SFTP: add copy() method (only usable if copy-data ext is available) (#​2101)

v3.0.46

Compare Source

• BigInteger/BCMath: strict_types fix (#​2089)

v3.0.45

Compare Source

• BigInteger: modPow() calls with negative base gave incorrect result (#​2086)
• BigInteger: barrett reduction returned '' vs '0' for bcmath engine (#​2087)

v3.0.44

Compare Source

• SSH2: add send_eof() method (#​2062)
• SSH2: server identification string handling enhancements (#​2082, #​2083)
• SSH2: shore up terrapin counter measures
• SSH2: fix for packets sent between KEXINIT packets (#​2084)
• SFTP: convert filenames to strings (#​2065)
• Hash: add cmac_aes algorithm (#​1967)
• ASN1: support tags with values >= 30 (#​2066)
• PublicKeyLoader: improve handling of bad keys (#​2077, #​2079)
• RSA: fix for keys with negative modulos (#​2085)
• BigInteger: adjust priority with which BCMath is used for PHP 8.4+

v3.0.43

Compare Source

• fix PHP 8.4 deprecations
• BigInteger: workaround for regression in GMP that PHP introduced
• BigInteger: speed up Barrett reductions
• X509: make the attributes section of new CSRs be blank (#​1522)
• X509: add getRequestedCertificateExtensions()
• X509: algorithmidentifier parameters could get incorrectly set (#​2051)
• SSH2: ignore <kex-strict-s-v00@​openssh.com> in key re-exchanges ([

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