Affected: OpenSSL

Issue summary: The implementations of AES-SIV (RFC 5297) and AES-GCM-SIV (RFC 8452) mishandle the authentication of AAD (Additional Authenticated Data) with an empty ciphertext allowing a forgery of such messages.

Impact summary: An attacker can forge empty messages with arbitrary AAD to the victim's application using these ciphers.

AES-SIV (RFC 5297) and AES-GCM-SIV (RFC 8452) are nonce-misuse-resistant AEAD modes: they accept a key, nonce, optional AAD (bytes that are authenticated but not encrypted), and plaintext, and produces ciphertext plus a 16-byte tag. On decrypt, `EVP_DecryptFinal_ex()` is documented to return success only if the tag is verified succesfully.

In OpenSSL's provider implementation of these ciphers, the expected tag is computed only when decryption function is invoked with non-empty data. If the caller supplies AAD and then calls `EVP_DecryptFinal_ex()` without invocation of the ciphertext update, which can happen when the received ciphertext length is zero, the tag is never recalculated and still holds its all-zeros value.

When AES-GCM-SIV is used, an attacker who sends arbitrary AAD, empty ciphertext, and all-zeros tag passes authentication under any key they do not know, single-shot. When AES-SIV is used, for mounting the attack it's necessary for the application to reuse the decryption context without resetting the key.

AES-SIV is implemented since OpenSSL 3.0. AES-GCM-SIV is implemented since OpenSSL 3.2.

No protocols implemented in OpenSSL…

Affected: Ubuntu:22.04:LTS: openssl, Ubuntu:24.04:LTS: openssl, Ubuntu:25.10: openssl, Ubuntu:26.04:LTS: openssl

Frank Buss discovered that OpenSSL had a heap buffer over-read in ASN.1 content parsing. An attacker could possibly use this issue to cause OpenSSL to crash, resulting in a denial of service, or obtain sensitive information. (CVE-2026-34180)

Pavol Zacik and Alex Gaynor discovered that OpenSSL incorrectly accepted PKCS#12 files with short HMAC keys when using PBMAC1. An attacker could possibly use this issue to bypass integrity checks. This issue only affected Ubuntu 25.10 and Ubuntu 26.04 LTS. (CVE-2026-34181)

Asim Viladi Oglu Manizada and Alex Gaynor discovered that OpenSSL could accept forged CMS AuthEnvelopedData messages. An attacker could possibly use this issue to bypass message authentication checks. (CVE-2026-34182)

Abhinav Agarwal discovered that OpenSSL had unbounded memory growth in the QUIC PATH_CHALLENGE handler. A remote attacker could possibly use this issue to cause OpenSSL to use excessive resources, leading to a denial of service. This issue only affected Ubuntu 25.10 and Ubuntu 26.04 LTS. (CVE-2026-34183)

Sunwoo Lee, Hyuk Lim, and Seunghyun Yoon discovered that OpenSSL had a NULL pointer dereference in QUIC server initial packet handling. A remote attacker could possibly use this issue to cause OpenSSL to crash, resulting in a denial of service. This issue only affected Ubuntu 25.10 and Ubuntu 26.04 LTS. (CVE-2026-42764)

Mayank Jangid, Kushal Khemka, Hari Priandana, Bhabani Sankar Das, and Qifan Zhang discovered that OpenSSL had a possible NULL derefe…