CVE-2023-49083: Cryptography.io Cryptography DoS Flaw

CVE-2023-49083 Overview

CVE-2023-49083 is a Null Pointer Dereference vulnerability affecting the popular Python cryptography package. The vulnerability occurs when calling load_pem_pkcs7_certificates or load_der_pkcs7_certificates functions, which can lead to a NULL-pointer dereference and subsequent segmentation fault. This flaw poses a serious Denial of Service (DoS) risk for any application attempting to deserialize PKCS#7 blobs or certificates.

Critical Impact

Exploitation of this vulnerability can cause application crashes and service disruption in any Python application using the cryptography library to process PKCS#7 certificates, potentially leading to widespread availability issues in production environments.

Affected Products

• cryptography.io cryptography (versions prior to 41.0.6)
• Python applications using cryptography package for PKCS#7 certificate handling
• Systems with cryptography library installed via pip or system package managers

Discovery Timeline

• 2023-11-27 - cryptography.io releases security patch in version 41.0.6
• 2023-11-29 - CVE-2023-49083 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2023-49083

Vulnerability Analysis

This vulnerability exists within the PKCS#7 certificate loading functionality of the Python cryptography library. When applications attempt to load malformed or specially crafted PKCS#7 certificates using either load_pem_pkcs7_certificates() or load_der_pkcs7_certificates() functions, the underlying code fails to properly validate the certificate data before processing. This results in a NULL pointer being dereferenced, causing an immediate segmentation fault and application crash.

The impact extends beyond simple crashes—in production environments where the cryptography library is used for certificate validation, authentication, or secure communication setup, this vulnerability can be weaponized to cause sustained service outages. Any network-facing service that processes user-supplied or external PKCS#7 certificates is particularly vulnerable.

Root Cause

The root cause is improper input validation in the PKCS#7 certificate parsing code. The functions load_pem_pkcs7_certificates and load_der_pkcs7_certificates do not adequately check for null or invalid pointers during certificate deserialization. When parsing certain malformed PKCS#7 bundles, internal data structures may not be properly initialized, leading to a null pointer that is subsequently dereferenced without validation. This is classified as CWE-476 (NULL Pointer Dereference).

Attack Vector

An attacker can exploit this vulnerability remotely by supplying a malicious PKCS#7 certificate blob to any application that uses the vulnerable functions to process certificates. The attack requires no authentication or special privileges—only the ability to submit certificate data to a vulnerable endpoint. Attack scenarios include:

• Submitting malformed certificates to web applications that verify client certificates
• Targeting email systems that process S/MIME signed messages (which use PKCS#7)
• Attacking API endpoints that accept certificate uploads for validation

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

Source: GitHub Commit

Detection Methods for CVE-2023-49083

Indicators of Compromise

• Application crashes or segmentation faults when processing PKCS#7 certificates
• Unexpected service restarts or container crashes in Python applications
• Core dump files containing stack traces pointing to cryptography library functions
• Log entries indicating segfault signals (SIGSEGV) in certificate processing workflows

Detection Strategies

• Audit installed Python packages using pip list or pip freeze to identify cryptography versions below 41.0.6
• Implement dependency scanning in CI/CD pipelines to detect vulnerable library versions
• Monitor application logs for segmentation fault errors during certificate operations
• Use software composition analysis (SCA) tools to track vulnerable dependencies across your environment

Monitoring Recommendations

• Configure crash monitoring and alerting for Python applications that handle certificates
• Implement application health checks that detect repeated crashes in certificate processing services
• Set up dependency vulnerability scanning as part of regular security assessments
• Monitor for unusual patterns of certificate submission that may indicate exploitation attempts

How to Mitigate CVE-2023-49083

Immediate Actions Required

• Upgrade the cryptography package to version 41.0.6 or later immediately using pip install --upgrade cryptography
• Verify the upgrade was successful by checking the installed version with pip show cryptography
• Restart any running applications or services that use the cryptography library to load the patched version
• Review application logs for evidence of prior exploitation attempts or unexplained crashes

Patch Information

The vulnerability has been patched in cryptography version 41.0.6, released on November 27, 2023. The fix adds proper null pointer validation during PKCS#7 certificate parsing to prevent the dereference of invalid pointers. The security fix is documented in the GitHub Security Advisory GHSA-jfhm-5ghh-2f97 and the patch can be reviewed in GitHub Pull Request #9926.

Distribution-specific patches are also available:

• Fedora Package Announcement
• Debian LTS Announcement

Workarounds

• Implement input validation to reject malformed PKCS#7 certificates before passing them to the vulnerable functions
• Add exception handling around certificate loading functions to catch and log crashes gracefully
• Consider using application-level sandboxing or process isolation to limit the impact of crashes
• Temporarily disable PKCS#7 certificate processing functionality if it is not critical to operations

# Upgrade cryptography package to patched version
pip install --upgrade cryptography>=41.0.6

# Verify installed version
pip show cryptography | grep Version

# For system-wide installation (requires root)
sudo pip install --upgrade cryptography>=41.0.6

# For requirements.txt, update the minimum version
echo "cryptography>=41.0.6" >> requirements.txt