CVE-2023-0217: OpenSSL DSA Public Key DoS Vulnerability

CVE-2023-0217 Overview

CVE-2023-0217 is a Null Pointer Dereference vulnerability affecting OpenSSL's EVP_PKEY_public_check() function. An invalid pointer dereference on read can be triggered when an application attempts to validate a malformed DSA public key, most likely resulting in an application crash. This function can be called on public keys supplied from untrusted sources, enabling remote attackers to cause a denial of service attack.

The TLS implementation in OpenSSL does not call this vulnerable function directly. However, applications may invoke EVP_PKEY_public_check() when additional security requirements are imposed by standards such as FIPS 140-3, expanding the potential attack surface for affected deployments.

Critical Impact

Remote attackers can trigger application crashes by supplying malformed DSA public keys to applications using EVP_PKEY_public_check(), causing denial of service conditions.

Affected Products

• OpenSSL (all vulnerable versions)
• Applications using EVP_PKEY_public_check() for DSA key validation
• Systems implementing FIPS 140-3 compliance with OpenSSL

Discovery Timeline

• 2023-02-07 - OpenSSL Security Advisory published
• 2023-02-08 - CVE-2023-0217 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2023-0217

Vulnerability Analysis

This vulnerability stems from improper handling of malformed DSA public key data within the EVP_PKEY_public_check() function. When the function processes a specially crafted DSA public key, it fails to properly validate the key structure before dereferencing internal pointers. This leads to an invalid pointer dereference on read, causing memory access violations that result in application termination.

The attack requires no authentication or user interaction, as the vulnerability can be exploited by simply providing a malformed DSA public key to an application that validates keys using the affected function. While the TLS handshake process in OpenSSL does not utilize this specific function, applications enforcing stricter security standards or performing additional key validation are vulnerable.

Root Cause

The root cause is a NULL pointer dereference (CWE-476) occurring when the OpenSSL library attempts to access memory through an invalid pointer during DSA public key validation. The code fails to perform adequate null checks before dereferencing pointers within the DSA key structure, leading to undefined behavior when processing malformed input.

Attack Vector

The attack vector is network-based with low complexity. An attacker can exploit this vulnerability by:

1. Crafting a malformed DSA public key with specific structural defects
2. Submitting this key to an application that calls EVP_PKEY_public_check() for validation
3. Triggering the invalid pointer dereference when the function processes the malicious input
4. Causing the target application to crash, resulting in denial of service

Applications implementing FIPS 140-3 compliance requirements or custom key validation workflows are particularly susceptible, as they are more likely to invoke the vulnerable function on untrusted key material.

Detection Methods for CVE-2023-0217

Indicators of Compromise

• Application crashes with segmentation faults during DSA key processing operations
• Core dumps showing null pointer dereference in OpenSSL's EVP_PKEY_public_check() call stack
• Unusual volume of DSA key validation requests from external sources
• Service availability disruptions coinciding with key processing operations

Detection Strategies

• Monitor application logs for segmentation faults and crash events related to OpenSSL functions
• Implement input validation and sanitization for all DSA public keys before passing to OpenSSL
• Deploy application-level monitoring to detect unusual patterns in key validation requests
• Use memory debugging tools in development environments to identify similar pointer issues

Monitoring Recommendations

• Configure crash dump collection and analysis for applications using OpenSSL key validation
• Establish baseline metrics for key validation operations to detect anomalous activity
• Monitor network traffic for suspicious patterns in key submission attempts
• Implement alerting for repeated application restarts that may indicate exploitation attempts

How to Mitigate CVE-2023-0217

Immediate Actions Required

• Update OpenSSL to the latest patched version immediately
• Identify all applications in your environment that call EVP_PKEY_public_check()
• Implement rate limiting on endpoints that accept and validate public keys
• Consider temporarily disabling DSA key validation if not required for operations

Patch Information

OpenSSL has released security updates to address this vulnerability. The fix is available in the OpenSSL Commit Diff (commit 23985bac83fd50c8e29431009302b5442f985096). Organizations should review the OpenSSL Security Advisory 20230207 for version-specific guidance. Additional vendor advisories are available from Gentoo Security Advisory GLSA-202402-08 and SonicWall Vulnerability SNWLID-2023-0003.

Workarounds

• Avoid calling EVP_PKEY_public_check() on DSA keys from untrusted sources until patched
• Implement pre-validation checks on key structure before passing to OpenSSL functions
• Use alternative key validation methods that do not rely on the vulnerable function
• Deploy web application firewalls or input filtering to reject malformed key submissions

# Configuration example
# Check current OpenSSL version
openssl version -a

# Verify OpenSSL package version on Debian/Ubuntu
dpkg -l | grep openssl

# Verify OpenSSL package version on RHEL/CentOS
rpm -qa | grep openssl

# Update OpenSSL on Debian/Ubuntu
sudo apt-get update && sudo apt-get upgrade openssl

# Update OpenSSL on RHEL/CentOS
sudo yum update openssl