CVE-2026-75803
Issue summary: ChaCha20-Poly1305 and AES-OCB decryption with an empty
ciphertext can report success without verifying the supplied authentication
tag when the operation is finalized by calling the EVP_Cipher() function.
Impact summary: Applications calling EVP_Cipher() on an empty ciphertext and
expecting the call to check the AEAD tag may accept forged messages.
CWE: CWE-354 (Improper Validation of Integrity Check Value)
Description: The EVP_Cipher() API call for AEAD ciphers behaves like a one
shot encryption and decryption call. It also verifies the AEAD tag after the
decryption operation. However for AES-OCB and ChaCha20-Poly1305 ciphers
it skipped the AEAD tag verification when an empty ciphertext was passed to
the function. The callers of this function might believe that a successful
return indicates a valid AEAD tag for these ciphers, even when that has not
truly been validated in this case.
FIPS impact: no
The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this CVE
as the affected algorithms are not FIPS approved and thus not implemented
in the FIPS module.
CSIRTS triage
- What
- Multiple denial of service vulnerabilities in OpenSSL QUIC and DTLS handling allow remote attackers to exhaust resources or crash the service through malformed packets.
- Who is affected
- Ubuntu 26.04 LTS systems and applications using affected OpenSSL versions with QUIC or DTLS functionality enabled.
- Urgency
- Moderate; allows denial of service but not code execution; no active exploitation reported.
- Action
- Apply the USN-8678-1 OpenSSL security update to affected Ubuntu systems.
AI-assisted analysis generated from the source advisory — verify against the original.
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Advisory coverage (3)
- unknownUSN-8678-1: OpenSSL vulnerabilitiesubuntu · 2026-08-25
- unknownCVE-2026-75803: Issue summary: ChaCha20-Poly1305 and AES-OCB decryption with an empty ciphertext can report su…nvd · 2026-08-25
- unknownDSA-6465-1 openssl - security updatedebian · 2026-08-25
External references
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