CVE-2023-0216: OpenSSL PKCS7 DoS Vulnerability

CVE-2023-0216 Overview

CVE-2023-0216 is a null pointer dereference vulnerability in OpenSSL that can be triggered when an application attempts to load malformed PKCS7 data using the d2i_PKCS7(), d2i_PKCS7_bio(), or d2i_PKCS7_fp() functions. This vulnerability results in an application crash, which could lead to a denial of service condition against affected systems.

While OpenSSL's TLS implementation does not directly call these vulnerable functions, third-party applications that process untrusted PKCS7 data are at risk. PKCS7 is commonly used for cryptographic message syntax, including signed and encrypted data formats, making this vulnerability relevant to applications handling certificates, signatures, or encrypted messages from external sources.

Critical Impact

Remote attackers can crash applications processing PKCS7 data by supplying specially crafted malformed input, causing denial of service without requiring authentication.

Affected Products

• OpenSSL (versions prior to patched releases)
• Stormshield Stormshield Management Center
• Third-party applications using vulnerable OpenSSL PKCS7 parsing functions

Discovery Timeline

• 2023-02-08 - CVE-2023-0216 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2023-0216

Vulnerability Analysis

This vulnerability is classified as CWE-476 (NULL Pointer Dereference). The flaw occurs when OpenSSL's PKCS7 parsing functions encounter malformed data structures that cause an invalid pointer to be dereferenced during a read operation. The underlying issue stems from insufficient validation of PKCS7 data structures before pointer operations are performed.

The attack requires no privileges and no user interaction, making it particularly concerning for services that automatically process PKCS7 data from untrusted sources. The vulnerability exclusively affects availability—it cannot be used to exfiltrate data or modify system state, but the resulting crash can disrupt service operations.

Root Cause

The root cause lies in OpenSSL's PKCS7 data parsing logic, where certain malformed input sequences can lead to an invalid pointer state. When the d2i_PKCS7() family of functions attempts to parse specially crafted PKCS7 structures, the code performs a read operation on a pointer that has not been properly validated, resulting in a null pointer dereference.

The PKCS7 parsing code did not adequately verify the integrity and structure of input data before performing memory operations, allowing attackers to trigger the crash condition by providing intentionally malformed data that passes initial validation but creates an invalid pointer state during subsequent processing.

Attack Vector

The attack vector is network-based, allowing remote exploitation without authentication. An attacker can exploit this vulnerability by:

1. Identifying an application that uses OpenSSL's PKCS7 parsing functions to process external data
2. Crafting a malformed PKCS7 data blob designed to trigger the invalid pointer dereference
3. Sending the malicious data to the target application through any input channel that feeds into the vulnerable functions
4. Causing the application to crash when it attempts to parse the malformed data

The vulnerability is particularly relevant for applications that handle S/MIME email messages, signed documents, or certificate chains from untrusted sources. Services that automatically process such data without prior validation are most at risk.

Detection Methods for CVE-2023-0216

Indicators of Compromise

• Application crashes with segmentation faults in OpenSSL PKCS7 parsing functions
• Core dumps showing null pointer dereference in d2i_PKCS7(), d2i_PKCS7_bio(), or d2i_PKCS7_fp() call stacks
• Unexpected service restarts correlated with processing of external PKCS7 data
• Log entries indicating malformed PKCS7 data received prior to service failures

Detection Strategies

• Monitor application logs and system crash reports for segmentation faults related to OpenSSL PKCS7 operations
• Implement input validation to detect and reject malformed PKCS7 structures before passing to OpenSSL functions
• Deploy intrusion detection rules to identify anomalous PKCS7 data patterns in network traffic
• Use application performance monitoring to detect unusual crash patterns in services handling cryptographic data

Monitoring Recommendations

• Enable crash reporting and core dump analysis for applications using OpenSSL
• Set up alerts for service availability interruptions in systems processing PKCS7 data
• Monitor OpenSSL library version usage across the infrastructure to identify vulnerable deployments
• Track patch status for OpenSSL dependencies in all applications and container images

How to Mitigate CVE-2023-0216

Immediate Actions Required

• Upgrade OpenSSL to the latest patched version addressing CVE-2023-0216
• Audit all applications to identify those using d2i_PKCS7(), d2i_PKCS7_bio(), or d2i_PKCS7_fp() functions
• Implement input validation for PKCS7 data from untrusted sources where possible
• Consider temporarily disabling or restricting services that process untrusted PKCS7 data until patches can be applied

Patch Information

OpenSSL has released security updates to address this vulnerability. The fix is available in the OpenSSL Commit Diff (commit 934a04f0e775309cadbef0aa6b9692e1b12a76c6). Organizations should apply the patch by upgrading to the fixed OpenSSL version appropriate for their deployment.

Additional vendor-specific advisories are available:

• OpenSSL Security Advisory
• Gentoo GLSA 202402-08
• SonicWall PSIRT Vulnerability SNWLID-2023-0003

Workarounds

• Restrict processing of PKCS7 data to trusted sources only until patches can be applied
• Implement application-level input size limits and basic structure validation before OpenSSL processing
• Deploy web application firewalls or network security controls to filter potentially malicious PKCS7 content
• Use process isolation or sandboxing for applications that must process untrusted PKCS7 data

# Check OpenSSL version for vulnerability assessment
openssl version -a

# Verify the patched commit is present (if building from source)
git log --oneline | grep 934a04f0e775309cadbef0aa6b9692e1b12a76c6