OpenSSL’s CMS implementation does not properly verify the cipher algorithm and tag length fields in AuthEnvelopedData messages. An attacker can transmit a forged CMS message that specifies a non‑authenticated cipher or a shortened tag length. The library in this configuration will still decrypt the message and report success, yielding decryption capability for a legitimate recipient key or bypassing authenticity checks. The impact is that modified data can be processed as if it were genuine and that an attacker may recover the equivalent decryption key for a given recipient.

The flaw affects the OpenSSL library. No specific product versions are listed by the CNA; therefore any OpenSSL installation that processes CMS data is potentially impacted.

The advisory references CWE-354, a weakness in authentication and integrity checks, but does not provide a CVSS score, EPSS score, or KEV status. The described attack scenarios require an attacker who can intercept, modify, or replay CMS traffic, indicating that the vulnerability is exploitable in environments that use CMS. Given the absence of severity metrics, the risk remains uncertain, but the potential for key-equivalent compromise and integrity bypass supports the recommendation to address the issue promptly.