Cherry-Pick fix for CVE-2023-49083 from (pyca#9927)

* Fixed crash when loading a PKCS#7 bundle with no certificates (pyca#9926)
pyca#9926

CHANGELOG.rst

@@ -1,6 +1,15 @@
 Changelog
 =========
 
+.. _v3-3-2-1:
+
+3.3.2.1 - 2024-01-18
+~~~~~~~~~~~~~~~~~~~~
+
+* Fixed a null-pointer-dereference and segfault that could occur when loading
+  certificates from a PKCS#7 bundle.  Credit to **pkuzco** for reporting the
+  issue. **CVE-2023-49083**
+
 .. _v3-3-2:
 
 3.3.2 - 2021-02-07

docs/spelling_wordlist.txt

@@ -35,6 +35,7 @@ decrypted
 decrypting
 deprecations
 DER
+dereference
 deserialize
 deserialized
 Deserialization

src/cryptography/__about__.py

@@ -22,7 +22,7 @@
 )
 __uri__ = "https://github.com/pyca/cryptography"
 
-__version__ = "3.3.2"
+__version__ = "3.3.2.1"
 
 __author__ = "The cryptography developers"
 __email__ = "cryptography-dev@python.org"

src/cryptography/hazmat/backends/openssl/backend.py

@@ -2664,9 +2664,12 @@ def _load_pkcs7_certificates(self, p7):
                 _Reasons.UNSUPPORTED_SERIALIZATION,
             )
 
+        certs = []
+        if p7.d.sign == self._ffi.NULL:
+            return certs
+
         sk_x509 = p7.d.sign.cert
         num = self._lib.sk_X509_num(sk_x509)
-        certs = []
         for i in range(num):
             x509 = self._lib.sk_X509_value(sk_x509, i)
             self.openssl_assert(x509 != self._ffi.NULL)

tests/hazmat/primitives/test_pkcs7.py

@@ -80,6 +80,12 @@ def test_load_pkcs7_unsupported_type(self):
                 mode="rb",
             )
 
+    def test_load_pkcs7_empty_certificates(self, backend):
+        der = b"\x30\x0B\x06\x09\x2A\x86\x48\x86\xF7\x0D\x01\x07\x02"
+
+        certificates = pkcs7.load_der_pkcs7_certificates(der)
+        assert certificates == []
+
 
 # We have no public verification API and won't be adding one until we get
 # some requirements from users so this function exists to give us basic

vectors/cryptography_vectors/__about__.py

@@ -20,7 +20,7 @@
 
 __uri__ = "https://github.com/pyca/cryptography"
 
-__version__ = "3.3.2"
+__version__ = "3.3.2.1"
 
 __author__ = "The cryptography developers"
 __email__ = "cryptography-dev@python.org"