CVE-2026-54876 Client-Side Memory Leak in OCSP Response Checking
A malicious TLS server can cause memory exhaustion in clients with OCSP checking enabled, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-54876?
CVE-2026-54876 is a high-severity denial of service vulnerability in OpenSSL, published on 5 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-401
Which versions are affected by CVE-2026-54876?
Linux distribution packages (4)
openssl3 Red Hat:hummingbird:1 | All versions | 0:3.5.7-2.2.hum1 |
openssl3-devel Red Hat:hummingbird:1 | All versions | 0:3.5.7-2.2.hum1 |
openssl3-devel-engine Red Hat:hummingbird:1 | All versions | 0:3.5.7-2.2.hum1 |
openssl3-libs Red Hat:hummingbird:1 | All versions | 0:3.5.7-2.2.hum1 |
How do I fix CVE-2026-54876?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-54876 being exploited?
There is no known exploitation of CVE-2026-54876 in the wild and no public exploit code.
Sources
Also known as CLEANSTART-2026-WR38385, DEBIAN-CVE-2026-54876, GHSA-5cfw-78wc-wvjq, RHSA-2026:57021, UBUNTU-CVE-2026-54876.