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Moderate severityNVD Advisory· Published Nov 29, 2023· Updated Dec 18, 2025

cryptography vulnerable to NULL-dereference when loading PKCS7 certificates

CVE-2023-49083

Description

cryptography is a package designed to expose cryptographic primitives and recipes to Python developers. Calling load_pem_pkcs7_certificates or load_der_pkcs7_certificates could lead to a NULL-pointer dereference and segfault. Exploitation of this vulnerability poses a serious risk of Denial of Service (DoS) for any application attempting to deserialize a PKCS7 blob/certificate. The consequences extend to potential disruptions in system availability and stability. This vulnerability has been patched in version 41.0.6.

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

Calling load_pem_pkcs7_certificates or load_der_pkcs7_certificates in the Python cryptography library before 41.0.6 can cause a NULL-pointer dereference and segfault, leading to a denial of service.

Vulnerability

Description

The Python cryptography library, which provides cryptographic primitives and recipes, contains a NULL-pointer dereference vulnerability in functions load_pem_pkcs7_certificates and load_der_pkcs7_certificates [1]. These functions are used to deserialize PKCS7 certificate bundles from PEM or DER formats. The flaw occurs when processing a PKCS7 blob that contains no certificates; the underlying OpenSSL code returns a NULL pointer in p7.d.sign, and prior to the fix, the library did not check for this condition before dereferencing the pointer [2][4].

Exploitation and

Attack Surface

An attacker can exploit this vulnerability by providing a specially crafted PKCS7 input (either PEM or DER) that triggers the NULL-pointer dereference. No authentication is required; the attack is entirely remote if an application accepts untrusted PKCS7 data. As demonstrated in the advisory, a minimal payload such as MAsGCSqGSIb3DQEHAg== (PEM) or its DER equivalent is sufficient to cause a crash [4]. Any Python application using these functions to load certificates from untrusted sources is vulnerable.

Impact

Successful exploitation results in a segmentation fault, leading to denial of service (DoS) [1]. This can disrupt system availability and stability, making the application unresponsive or terminating it entirely. The vulnerability is classified with a CVSS score of 7.5 (HIGH) due to its low attack complexity and network-based vector causing complete availability impact.

Mitigation

Status

The vulnerability has been patched in cryptography version 41.0.6, released on 2023-11-27 [1][2][3]. The fix adds a NULL check on p7.d.sign before accessing its cert member, returning an empty list if the pointer is NULL [3]. All users should upgrade to version 41.0.6 or later. There are no known workarounds; applications that cannot upgrade should avoid processing untrusted PKCS7 input.

References
  1. NVD - CVE-2023-49083
  2. Fixed crash when loading a PKCS#7 bundle with no certificates by alex · Pull Request #9926 · pyca/cryptography
  3. 41.0.6 release (#9927) · pyca/cryptography@f09c261
  4. security - Python Cryptography advisory: CVE-2023-49083 NULL-dereference when loading PKCS7 certificates

AI Insight generated on May 20, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.

Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
cryptographyPyPI
>= 3.1, < 41.0.641.0.6

Affected products

26

Patches

1
f09c261ca10a

41.0.6 release (#9927)

https://github.com/pyca/cryptographyAlex GaynorNov 27, 2023via ghsa
commit
9 files changed · +26 −5
  • CHANGELOG.rst+9 −0 modified
    @@ -1,6 +1,15 @@
 Changelog
 =========
 
+.. _v41-0-6:
+
+41.0.6 - 2023-11-27
+~~~~~~~~~~~~~~~~~~~
+
+* 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**
+
 .. _v41-0-5:
 
 41.0.5 - 2023-10-24
  • docs/spelling_wordlist.txt+1 −0 modified
    @@ -38,6 +38,7 @@ decrypted
 decrypting
 deprecations
 DER
+dereference
 deserialize
 deserialized
 Deserialization
  • pyproject.toml+1 −1 modified
    @@ -11,7 +11,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "cryptography"
-version = "41.0.5"
+version = "41.0.6"
 authors = [
     {name = "The Python Cryptographic Authority and individual contributors", email = "cryptography-dev@python.org"}
 ]
  • src/cryptography/__about__.py+1 −1 modified
    @@ -10,7 +10,7 @@
     "__copyright__",
 ]
 
-__version__ = "41.0.5"
+__version__ = "41.0.6"
 
 
 __author__ = "The Python Cryptographic Authority and individual contributors"
  • src/cryptography/hazmat/backends/openssl/backend.py+4 −1 modified
    @@ -1890,9 +1890,12 @@ def _load_pkcs7_certificates(self, p7) -> typing.List[x509.Certificate]:
                 _Reasons.UNSUPPORTED_SERIALIZATION,
             )
 
+        certs: list[x509.Certificate] = []
+        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)
  • src/rust/src/lib.rs+2 −0 modified
    @@ -3,6 +3,8 @@
 // for complete details.
 
 #![deny(rust_2018_idioms)]
+// Work-around for https://github.com/PyO3/pyo3/issues/3561
+#![allow(unknown_lints, clippy::unnecessary_fallible_conversions)]
 
 mod asn1;
 mod backend;
  • tests/hazmat/primitives/test_pkcs7.py+6 −0 modified
    @@ -89,6 +89,12 @@ def test_load_pkcs7_unsupported_type(self, backend):
                 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+1 −1 modified
    @@ -6,4 +6,4 @@
     "__version__",
 ]
 
-__version__ = "41.0.5"
+__version__ = "41.0.6"
  • vectors/pyproject.toml+1 −1 modified
    @@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "cryptography_vectors"
-version = "41.0.5"
+version = "41.0.6"
 authors = [
     {name = "The Python Cryptographic Authority and individual contributors", email = "cryptography-dev@python.org"}
 ]

Vulnerability mechanics

Generated on May 9, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.

References

10

News mentions

0

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