CVE-2022-4203: OpenSSL Certificate Verification DoS Flaw

CVE-2022-4203 Overview

CVE-2022-4203 is an Out-of-Bounds Read vulnerability affecting OpenSSL's X.509 certificate verification process, specifically in name constraint checking. This vulnerability occurs after certificate chain signature verification and requires either a Certificate Authority (CA) to have signed a malicious certificate or for the application to continue certificate verification despite failure to construct a path to a trusted issuer.

The read buffer overrun might result in a crash leading to a denial of service attack. In theory, it could also result in the disclosure of private memory contents such as private keys or sensitive plaintext, although no working exploit leading to memory contents disclosure has been publicly confirmed.

Critical Impact

A malicious TLS server can trigger this vulnerability in connecting clients, or a malicious client can trigger it against servers requesting client authentication, potentially causing denial of service or memory disclosure.

Affected Products

• OpenSSL (all vulnerable versions)
• TLS clients connecting to malicious servers
• TLS servers with client certificate authentication enabled

Discovery Timeline

• 2023-02-07 - OpenSSL releases security advisory
• 2023-02-24 - CVE CVE-2022-4203 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2022-4203

Vulnerability Analysis

This vulnerability exists within OpenSSL's X.509 certificate verification mechanism, specifically during the name constraint checking phase. Name constraints are an X.509 certificate extension that allows a CA to restrict the namespace within which subordinate CA certificates may issue certificates.

The flaw is an out-of-bounds read (CWE-125) that occurs when processing malformed certificates with specially crafted name constraints. The vulnerability requires specific conditions to be exploited: either a CA must have signed a malicious certificate, or the application must be configured to continue verification even when a trusted path cannot be constructed.

In practical attack scenarios, a malicious TLS server can exploit this vulnerability against connecting clients by presenting a crafted certificate. Conversely, if a TLS server requests client authentication, a malicious client can trigger the vulnerability by providing a malformed client certificate.

Root Cause

The root cause is improper bounds checking during the processing of name constraints in X.509 certificates. When OpenSSL parses and validates the name constraint extension, insufficient validation of input boundaries allows reading beyond the allocated buffer. This out-of-bounds read condition (CWE-125) can lead to accessing unintended memory regions during the certificate verification process.

Attack Vector

The attack is network-based and can be exploited in two primary scenarios:

Client-Side Attack: An attacker operates a malicious TLS server and waits for victims to connect. When a TLS client connects, the server presents a certificate with malformed name constraints, triggering the buffer overrun during verification.

Server-Side Attack: If a TLS server is configured to request client authentication, an attacker can connect as a malicious client and present a certificate designed to trigger the vulnerability during server-side verification.

The vulnerability requires the attacker to have either obtained a certificate signed by a trusted CA or to target applications that continue verification despite path construction failures.

Detection Methods for CVE-2022-4203

Indicators of Compromise

• Unexpected crashes in applications using OpenSSL for TLS connections
• Abnormal memory access patterns in OpenSSL processes during certificate verification
• Suspicious TLS connections presenting certificates with unusual name constraint extensions
• Application crashes coinciding with inbound or outbound TLS handshakes

Detection Strategies

• Monitor for OpenSSL process crashes during TLS handshakes, particularly during certificate verification phases
• Implement network monitoring to identify TLS sessions with anomalous certificate characteristics
• Deploy intrusion detection rules to flag certificates with malformed or suspicious name constraint extensions
• Enable detailed logging of certificate validation failures and errors

Monitoring Recommendations

• Configure crash reporting and core dump analysis for applications using vulnerable OpenSSL versions
• Monitor system logs for certificate verification errors related to name constraints
• Implement TLS inspection where appropriate to identify potentially malicious certificates
• Track application stability metrics for services handling TLS connections

How to Mitigate CVE-2022-4203

Immediate Actions Required

• Update OpenSSL to a patched version immediately
• Review and inventory all systems and applications using OpenSSL for TLS operations
• Prioritize patching TLS servers with client authentication enabled and TLS clients connecting to untrusted servers
• Consider temporarily disabling client certificate authentication on critical servers until patches are applied

Patch Information

OpenSSL has released security patches to address this vulnerability. The fix is available in the OpenSSL Commit Diff (commit c927a3492698c254637da836762f9b1f86cffabc). Detailed information about the vulnerability and remediation is available in the OpenSSL Security Advisory.

Additional vendor advisories are available from Gentoo GLSA 202402-08 and SonicWall SNWLID-2023-0003.

Workarounds

• Limit TLS client connections to trusted servers only where possible
• Disable client certificate authentication on servers where it is not strictly required
• Implement network segmentation to reduce exposure of vulnerable services
• Consider using a TLS-terminating proxy with a patched OpenSSL version in front of vulnerable applications

Applying the official OpenSSL patch is the recommended and most effective remediation. Organizations should follow their standard patch management procedures while prioritizing internet-facing services and applications handling sensitive data.