CVE-2026-31789

During the conversion of OCTET STRING values to hex strings, the required buffer size is calculated as the product of input data length multiplied by 3. On 32-bit platforms, this multiplication can cause an integer overflow, resulting in allocation of a buffer that is too small, followed by a write beyond its boundaries (heap buffer overflow). An attacker can provide a crafted X.509 certificate containing an excessively large OCTET STRING value in extensions such as Subject Key Identifier (SKID) or Authority Key Identifier (AKID). The vulnerability is triggered when an application or service displays or logs the contents of an untrusted X.509 certificate.

An attacker can cause an application processing a certificate to crash or—under specific circumstances—achieve arbitrary code execution (RCE) or other undefined behavior. Only 32-bit platforms are affected.

Apply patches available from the vendor according to the references (commits published in the OpenSSL GitHub repository). If immediate updating is not possible, avoid logging or displaying the contents of untrusted X.509 certificates on 32-bit platforms.

OpenSSL on 32-bit platforms—applications and services printing or logging the contents of untrusted X.509 certificates. FIPS modules in versions 3.6, 3.5, 3.4, 3.3, and 3.0 are not affected because the vulnerable code is outside the FIPS module boundary. Specific vulnerable versions are indicated in the vendor's references.