CVE-2026-42765 NULL Dereference in Certificate Verification with OCSP Checking
Attackers can cause a denial of service in applications using OpenSSL if they enable specific non-default certificate verification flags.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42765?
CVE-2026-42765 is a high-severity vulnerability in Openssl Openssl, published on 9 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Issue summary: When a partial-chain certificate verification is enabled together with OCSP response checking for the whole chain, a NULL dereference will happen if the verified chain does not have a self-signed trusted anchor, crashing the process.
Impact summary: A NULL pointer dereference can trigger a crash which leads to a Denial of Service for an application.
When performing OCSP response checking for certificates in the verification chain, the code always tries to access the next certificate as the issuer. There is a check for a self-signed certificate. However with the partial chain verification enabled when the chain does not have a self-signed trusted anchor, the issuer will be NULL for the last certificate in the chain. A NULL pointer dereference then happens.
This issue affects only applications which enable both OCSP verification of the certificate chain (X509_V_FLAG_OCSP_RESP_CHECK_ALL) and partial chain verification (X509_V_FLAG_PARTIAL_CHAIN) in the certificate verification. Both flags are disabled by default. For that reason, we have assigned Low severity to the issue.
No FIPS modules are affected by this issue as the affected code is outside the OpenSSL FIPS module boundary.
Weakness: CWE-476
Which versions are affected by CVE-2026-42765?
It affects 1 product.
Products include Openssl Openssl.
How do I fix CVE-2026-42765?
Apply the vendor's patch.
Is CVE-2026-42765 being exploited?
There is no known exploitation of CVE-2026-42765 in the wild and no public exploit code.
Other vulnerabilities in Openssl Openssl
Sources
Also known as DEBIAN-CVE-2026-42765, GHSA-vm8w-j6fw-jc7r, UBUNTU-CVE-2026-42765.