CVE-2003-0545: OpenSSL double free via malformed client certificate ASN.1 encoding

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 18 September 2026. Confidence: medium.

critical priorityCVSS 3.1 is 9.8 with network reachability, no privileges or interaction, and high impact across all three categories, and EPSS is near the top percentile despite no KEV listing.

What it is

OpenSSL 0.9.7 contains a double free vulnerability triggered by an SSL client certificate carrying a certain invalid ASN.1 encoding. Because the flaw sits in certificate parsing, a remote peer can reach it during the TLS handshake, and the double free can crash the process and possibly allow code execution.

Impact

An attacker can cause a denial of service by crashing the OpenSSL-using service, and the double free may permit arbitrary code execution in the affected process. The CVSS 3.1 vector rates confidentiality, integrity and availability impact all as high.

Attack surface

Reached remotely over the network during the SSL/TLS handshake when a client certificate is processed; the CVSS vector shows no privileges required and no user interaction. Any service that accepts client certificates with a vulnerable OpenSSL build is exposed.

Exploitation

Not listed in CISA KEV and no ransomware usage is documented, but EPSS is very high at 0.875 (99.7th percentile), indicating strong predicted exploitation activity. References include vendor and CERT advisories plus patch errata, but no public exploit tag is present in the record.

What to do

• Upgrade OpenSSL to a version later than 0.9.7 that contains the fix, or apply the vendor patch referenced in the Red Hat and UNIRAS advisories.
• If immediate patching is not possible, disable client certificate authentication or require it only from trusted peers to remove the trigger path.
• Rebuild or relink applications that statically bundle OpenSSL so the patched library is actually in use.
• Monitor vendor advisories for downstream distributions (Debian, Red Hat, IBM) and apply their updated packages.

Detection

• Watch for repeated TLS handshake failures or process crashes in services that accept client certificates.
• Monitor for core dumps or abnormal termination of OpenSSL-linked daemons and correlate with inbound TLS connections.
• Log and alert on client certificates with malformed or unusual ASN.1 encodings presented during handshakes.
• Track OpenSSL library versions in use across the estate to find hosts still running 0.9.7.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.