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HIGH

Client-Side Memory Leak in OCSP Response Checking

Published Aug 5, 2026

Description

Issue 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.

Impact summary: An attacker can leak an attacker-tunable amount of memory per TLS handshake in a victim client application. A long-running client that repeatedly connects to a malicious server can have its memory exhausted, resulting in a Denial of Service.

CWE: CWE-401: Missing Release of Memory after Effective Lifetime

Description: The affected function is called during X.509 certificate chain verification when OCSP response checking is enabled with the X509_V_FLAG_OCSP_RESP_CHECK or X509_V_FLAG_OCSP_RESP_CHECK_ALL verification flags, for example when a TLS client verifies an OCSP response stapled into the TLS handshake by the server.

When the received BasicOCSPResponse contains an empty SEQUENCE OF SingleResponse, which is permitted on the wire and accepted by the OpenSSL decoder, the OCSP_BASICRESP structure allocated by OCSP_response_get1_basic() was not freed because an early return bypassed the cleanup code at the end of the function.

The amount of memory leaked per handshake can be amplified by the attacker by padding the certs field of the BasicOCSPResponse with bogus certificates, which are parsed and stored in the leaked structure before the empty response check triggers the early return. 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.

FIPS impact: no

The FIPS modules in 4.0 and 3.6 are not affected by this issue as the affected code is outside the OpenSSL FIPS module boundary.

Affected products

Remediation

No remediation recorded yet.

Weaknesses (2)

CWE-401

CWE-772

References (8)

Change history (0)

No recorded changes yet.

Sources
CVE.org / MITRE
Status PUBLISHED
Assigner openssl
Published Aug 5, 2026
Updated Aug 5, 2026
Reserved Jun 16, 2026
Link CVE-2026-54876
CISA Vulnrichment
Updated Aug 5, 2026
NVD
Status Awaiting Analysis
Modified Aug 28, 2026
Link CVE-2026-54876
Red Hat
Severity Low
Public date Aug 5, 2026
Links CVE-2026-54876 - Bugzilla