OpenSSL’s CMS implementation fails to properly validate the cipher algorithm and tag length fields in AuthEnvelopedData messages, a classic example of CWE‑130 and CWE‑354, which concern inappropriate validation of cryptographic parameters and algorithm specifications. This flaw allows an attacker to forge a CMS message that specifies a non‑authenticated cipher or a shortened tag length. The library will still decrypt the message and report success, giving the attacker decryption capability for a legitimate recipient key or allowing an integrity bypass if the application trusts CMS_decrypt to reject modified content.

The vulnerability affects the OpenSSL library in any configuration that processes CMS data. No specific product versions are listed by the CNA; therefore any OpenSSL installation that implements the CMS API could be impacted. The FIPS modules are explicitly stated to be unaffected.

The CVSS score of 9.1 indicates a critical level of impact, while the EPSS score of <1% suggests that exploitation is currently uncommon. The vulnerability is not listed in the CISA KEV catalog. Exploitation requires an on‑path attacker who can intercept, modify, or replay CMS traffic, but once the flaw is leveraged the attacker can obtain key‑equivalent functionality or bypass integrity checks, which poses significant confidentiality and integrity risks.