CVE-2026-54876 OpenSSL CVE debrief

Who should care

Developers and administrators of TLS client applications that enable OCSP response checking should verify their configuration and take steps to mitigate the vulnerability. This includes verifying TLS client configuration to ensure OCSP response checking is disabled if not required. Additionally, monitoring client application memory usage for unusual patterns and implementing compensating controls to detect and prevent potential memory exhaustion attacks is recommended. Affected operators should review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance. They should also plan vendor-supported updates or mitigations through normal change control where exposure is confirmed and review compensating controls for exposed systems while remediation is scheduled and verified. Checking relevant monitoring, detection, and logs for exposed assets that need extra review is also crucial. Tracking exceptions, retesting remediated assets, and closing the item only after evidence is documented are important steps in the remediation process. Asset inventory and vulnerability management teams should be informed to ensure that affected systems are properly identified and prioritized for remediation. Security teams should also be aware of the potential impact on their organization's security posture and take appropriate measures to mitigate the risk. This may involve coordinating with vendors to obtain patches or implementing workarounds to reduce the risk of exploitation. By taking these steps, organizations can help protect their TLS client applications from potential memory exhaustion attacks. Security teams should also consider implementing additional security controls, such as rate limiting or IP blocking, to detect and prevent potential attacks. Furthermore, security teams should review their incident response plans to ensure that they are prepared to respond to potential security incidents related to this vulnerability. This includes having a plan in place to quickly identify and contain affected systems, as well as having a process for communicating with stakeholders about the incident. By being proactive and taking steps to

Technical summary

A malicious TLS server can cause a memory leak in a TLS client that has enabled OCSP response checking by sending an OCSP response that contains no single response entries. The affected function is called during X.509 certificate chain verification when OCSP response checking is enabled. The function fails to free the OCSP_BASICRESP structure when the received BasicOCSPResponse contains an empty SEQUENCE OF SingleResponse. The amount of memory leaked per handshake can be amplified by the attacker by padding the certs field of the BasicOCSPResponse with bogus certificates. A long-running TLS client that repeatedly connects to a malicious server can have its memory exhausted over time. OCSP response checking is not enabled by default. Only client applications that explicitly enable the OCSP response check verification flags are affected.

Defensive priority

TLS clients that enable OCSP response checking are vulnerable to a memory leak attack. Client applications should verify their TLS configuration and disable OCSP response checking if not required.

Recommended defensive actions

• Verify TLS client configuration to ensure OCSP response checking is disabled if not required.
• Monitor client application memory usage for unusual patterns.
• Implement compensating controls to detect and prevent potential memory exhaustion attacks.
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.

Evidence notes

The CVE description indicates a memory leak vulnerability in TLS clients that enable OCSP response checking. The vulnerability is caused by an affected function called during X.509 certificate chain verification. The function fails to free the OCSP_BASICRESP structure when the received BasicOCSPResponse contains an empty SEQUENCE OF SingleResponse.

Official resources