REDHAT-BUG-2481896: Medium severity OpenSSL OpenSSL vulnerability

AES-OCB IV Ignored on EVPCipher() Path

AES-OCB IV Ignored on EVPCipher() Path (CVE-2026-45445) Severity: Moderate

Issue summary: When an application drives an AES-OCB context through the public EVPCipher() one-shot interface, the application-supplied initialisation vector (IV) is silently discarded.

Impact summary: Every message encrypted under the same key uses the same effective nonce regardless of the IV supplied by the caller, resulting in (key, nonce) reuse and loss of confidentiality. If the same code path is used to compute the authentication tag, the tag depends only on the (key, IV) pair and not on the plaintext or ciphertext, allowing universal forgery of arbitrary ciphertext from a single captured message.

OpenSSL provides two ways to drive a cipher: the documented streaming interface (EVPCipherUpdate / EVPCipherFinalex) and a lower-level one-shot, EVPCipher(), whose documentation explicitly recommends against use by applications in favour of EVPCipherUpdate() and EVPCipherFinalex(). The OCB provider's streaming handler flushes the application-supplied IV into the OCB context before processing data; the one-shot handler did not. Every call to EVPCipher() on an AES-OCB context therefore ran with the all-zero key-derived offset state left by cipher initialisation, regardless of the caller's IV.

If EVPEncryptFinalex() is subsequently used to obtain the authentication tag, the deferred IV setup runs at that point and clears the running checksum that should have been accumulated over the plaintext. The resulting tag is a function of (key, IV) only and verifies against any ciphertext produced under the same (key, IV) pair.

The OpenSSL SSL/TLS implementation is not affected: AES-OCB is not a TLS cipher suite, and libssl does not call EVPCipher() in any case. Applications that drive AES-OCB through the documented streaming AEAD API (EVPCipherUpdate / EVPCipherFinalex) are not affected. Only applications that combine the AES-OCB cipher with the EVPCipher() one-shot API are vulnerable.

The FIPS modules in 4.0, 3.6, 3.5, 3.4 and 3.0 are not affected by this issue, as AES-OCB is outside the OpenSSL FIPS module boundary.

OpenSSL 4.0, 3.6, 3.5, 3.4 and 3.0 are vulnerable to this issue.

OpenSSL 1.1.1 and 1.0.2 are not affected by this issue: in those releases the IV is applied synchronously during cipher initialisation and the AES-OCB one-shot rejects data submitted before the IV is set.

OpenSSL 4.0 users should upgrade to OpenSSL 4.0.1. OpenSSL 3.6 users should upgrade to OpenSSL 3.6.3. OpenSSL 3.5 users should upgrade to OpenSSL 3.5.7. OpenSSL 3.4 users should upgrade to OpenSSL 3.4.6. OpenSSL 3.0 users should upgrade to OpenSSL 3.0.21.

This issue was reported on 16th April 2026 by Alex Gaynor (Anthropic). The fix was developed by Viktor Dukhovni.