Summary
When loading an (untrusted) XML document, for example the SAMLResponse, it's possible to induce an XXE.
$options is defined as:
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$options = LIBXML_DTDLOAD | LIBXML_DTDATTR | LIBXML_NONET | LIBXML_PARSEHUGE; |
including the DTDLoad option, which allows an attacker to read file contents from local file system OR internal network.
While there is the NONET option, an attacker can simply bypass if by using PHP filters:
php://filter/convert.base64-encode/resource=http://URL OR FILE
From there an attacker can induce network connections and steal the targeted file OOB (haven't fully tested this).
RCE may be possible with the php://expect or php://phar wrappers, but this hasn't been tested.
Note:
The mitigation here:
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foreach ($domDocument->childNodes as $child) { |
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if ($child->nodeType === XML_DOCUMENT_TYPE_NODE) { |
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throw new RuntimeException( |
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'Dangerous XML detected, DOCTYPE nodes are not allowed in the XML body' |
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); |
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} |
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} |
Comes too late, as the XML has already been loaded into a document.
Mitigation:
Remove the LIBXML_DTDLOAD | LIBXML_DTDATTR options.
Additionally, as a defense in depth measure, check if there is the string: <!DOCTYPE inside the XML before parsing it. (This is not a complete fix because someone may be able to exploit some parser differentials, to load a DOCTYPE, maybe through spacing like: <! DOCTYPE)
ahacker1-securesaml Reporter
Summary
When loading an (untrusted) XML document, for example the SAMLResponse, it's possible to induce an XXE.
$options is defined as:
saml2/src/SAML2/DOMDocumentFactory.php
Line 41 in 717c0ad
including the DTDLoad option, which allows an attacker to read file contents from local file system OR internal network.
While there is the NONET option, an attacker can simply bypass if by using PHP filters:
php://filter/convert.base64-encode/resource=http://URL OR FILE
From there an attacker can induce network connections and steal the targeted file OOB (haven't fully tested this).
RCE may be possible with the php://expect or php://phar wrappers, but this hasn't been tested.
Note:
The mitigation here:
saml2/src/SAML2/DOMDocumentFactory.php
Lines 63 to 69 in 717c0ad
Comes too late, as the XML has already been loaded into a document.
Mitigation:
Remove the LIBXML_DTDLOAD | LIBXML_DTDATTR options.
Additionally, as a defense in depth measure, check if there is the string: <!DOCTYPE inside the XML before parsing it. (This is not a complete fix because someone may be able to exploit some parser differentials, to load a DOCTYPE, maybe through spacing like: <! DOCTYPE)