A use-after-free vulnerability exists in OpenSSL's PKCS#7 signature verification when processing a specially crafted PKCS#7 or S/MIME signed message with an empty ASN.1 SET in the SignedData digestAlgorithms field. OpenSSL may incorrectly free a caller-owned BIO during PKCS7_verify(), and subsequent use of this BIO by the application results in a use-after-free condition. This can cause process crashes, heap corruption, or potentially remote code execution depending on allocator behavior and application BIO usage. Applications using OpenSSL PKCS#7 APIs are affected; those using CMS APIs or FIPS modules (versions 4.0, 3.6, 3.5, 3.4, 3.0) are not affected. The OpenSSL Software Foundation has released patches addressing this issue, as documented in multiple commits and a security advisory dated 2026-06-09.

The vulnerability can lead to process crashes, heap corruption, or potentially remote code execution when processing malicious PKCS#7 or S/MIME signed messages. This affects applications using OpenSSL PKCS#7 APIs. The severity is high given the potential for remote code execution, but exploitation depends on application-specific usage patterns and allocator behavior. CMS API users and OpenSSL FIPS modules are not impacted.

An official fix is available from the OpenSSL Software Foundation. Users and application developers should apply the patches provided in the OpenSSL commits referenced in the advisory (dated 2026-06-09). Applications using CMS APIs or OpenSSL FIPS modules are not affected and require no action. Verify that your OpenSSL version includes the fix by consulting the OpenSSL security advisory and applying updates accordingly.