CVE-2026-28388 NULL Pointer Dereference When Processing a Delta CRL
Attackers can cause a denial of service in applications using OpenSSL by providing a malformed delta CRL when specific verification flags are enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-28388?
CVE-2026-28388 is a high-severity vulnerability in Openssl Openssl, published on 7 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Issue summary: When a delta CRL that contains a Delta CRL Indicator extension is processed a NULL pointer dereference might happen if the required CRL Number extension is missing.
Impact summary: A NULL pointer dereference can trigger a crash which leads to a Denial of Service for an application.
When CRL processing and delta CRL processing is enabled during X.509 certificate verification, the delta CRL processing does not check whether the CRL Number extension is NULL before dereferencing it. When a malformed delta CRL file is being processed, this parameter can be NULL, causing a NULL pointer dereference.
Exploiting this issue requires the X509_V_FLAG_USE_DELTAS flag to be enabled in the verification context, the certificate being verified to contain a freshestCRL extension or the base CRL to have the EXFLAG_FRESHEST flag set, and an attacker to provide a malformed CRL to an application that processes it.
The vulnerability is limited to Denial of Service and cannot be escalated to achieve code execution or memory disclosure. For that reason the issue was assessed as Low severity according to our Security Policy.
The FIPS modules in 3.6, 3.5, 3.4, 3.3 and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.
Weakness: CWE-476
Which versions are affected by CVE-2026-28388?
It affects 1 product.
Products include Openssl Openssl.
How do I fix CVE-2026-28388?
Apply the vendor's patch.
Is CVE-2026-28388 being exploited?
There is no known exploitation of CVE-2026-28388 in the wild and no public exploit code.
Other vulnerabilities in Openssl Openssl
Sources
Also known as ALPINE-CVE-2026-28388, AZL-81953, AZL-82100, BELL-CVE-2026-28388, CLSA-2026-1778020035, CLSA-2026-1778020314 and 17 more.