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OpenSSL AES-OCB IV Ignored on EVP_Cipher() Path

IdentifiersCVE-2026-45445CWE-323

CVE-2026-45445 is a flaw in OpenSSL's AES-OCB implementation when driven through the public one-shot EVP_Cipher() API. In affected versions, the application-supplied IV is silently discarded on the EVP_Cipher() path because the OCB provider's one-shot handler fails to flush the caller-provided IV into the OCB context before processing data. As a result, each encryption operation runs with the all-zero key-derived offset state left by cipher initialization rather than the supplied nonce. This causes every message encrypted under the same key to use the same effective nonce. Additionally, if EVP_EncryptFinal_ex() is then used to obtain the authentication tag, deferred IV setup occurs at finalization time and clears the running checksum that should reflect the plaintext, causing the resulting tag to depend only on the key and IV rather than the plaintext or ciphertext. The issue affects OpenSSL 4.0.0 before 4.0.1, 3.6.0 before 3.6.3, 3.5.0 before 3.5.7, 3.4.0 before 3.4.6, and 3.0.0 before 3.0.21. OpenSSL SSL/TLS is not affected, and applications using the documented streaming interface EVP_CipherUpdate()/EVP_CipherFinal_ex() are not vulnerable.

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ANALYST BRIEF

Impact, mitigation & remediation

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Impact

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Successful exploitation breaks the security guarantees of AES-OCB for affected applications. Because the supplied IV is ignored, messages encrypted under the same key reuse the same effective nonce, resulting in loss of confidentiality. Where the same flawed code path is used to generate authentication tags, the tag can become a function only of the key and IV and not of the protected message contents, enabling universal forgery of arbitrary ciphertext under the same key/IV context from a single captured message. This can permit attackers to decrypt relationships between messages, tamper with protected data, and bypass authenticity and integrity protections in applications relying on AES-OCB via the one-shot API.

Mitigation

If you can’t patch tonight, do this now.

Do not use AES-OCB with the EVP_Cipher() one-shot API. Where immediate patching is not possible, migrate affected code paths to the documented streaming interface EVP_CipherUpdate()/EVP_CipherFinal_ex() for AES-OCB operations. If AES-OCB one-shot usage cannot be eliminated promptly, disable or avoid that functionality and rotate any keys used by vulnerable code paths after remediation because prior ciphertexts may have been produced with nonce reuse. OpenSSL's SSL/TLS stack is not affected, and the FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected because AES-OCB is outside the FIPS module boundary.

Remediation

Patch, then assume compromise.

Upgrade OpenSSL to a fixed release: 4.0.1 or later, 3.6.3 or later, 3.5.7 or later, 3.4.6 or later, or 3.0.21 or later, as appropriate for the deployed branch. In addition to patching the library, affected applications should be reviewed and refactored to avoid using AES-OCB through the EVP_Cipher() one-shot API. Use the documented streaming AEAD interface instead, specifically EVP_CipherUpdate() together with EVP_CipherFinal_ex(), to ensure IV handling and authentication processing are correct.
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EXPOSURE SURFACE

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VendorProductType
FreebsdFreebsdapplication
OpenSSL Software FoundationOpensslapplication

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