CVE-2026-45446

Incorrect Tag Processing for Empty Messages in AES-GCM-SIV and AES-SIV modes

Published Jun 9, 2026 CVSS 3.1 · 4.8 Medium EPSS < 1% KEV · Not listed
Description
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 itself (TLS/CMS/PKCS7/HPKE/QUIC) support
either AES-GCM-SIV or AES-SIV. To mount an attack, the applications must
implement their own protocol and use the EVP interface. Also they must skip the
ciphertext update when a message with an empty ciphertext arrives.

The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this
issue, as these algorithms are not FIPS approved and the affected code is
outside the OpenSSL FIPS module boundary.

Remediation

No solution or workaround provided in the CVE record

Tracking

Sign in to view the affected projects.

Advisories

Source ID Title
Debian DSA Debian DSA DSA-6335-1 openssl security update
Ubuntu USN Ubuntu USN USN-8414-1 OpenSSL vulnerabilities
History
Type Values Removed Values Added
CPEs cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
cpe:2.3:a:openssl:openssl:4.0.0:-:*:*:*:*:*:*
Type Values Removed Values Added
Metrics cvssV3_1

{'score': 4.8, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N'}

ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Openssl
Openssl openssl
Vendors & Products Openssl
Openssl openssl
Type Values Removed Values Added
Description 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 itself (TLS/CMS/PKCS7/HPKE/QUIC) support either AES-GCM-SIV or AES-SIV. To mount an attack, the applications must implement their own protocol and use the EVP interface. Also they must skip the ciphertext update when a message with an empty ciphertext arrives. The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this issue, as these algorithms are not FIPS approved and the affected code is outside the OpenSSL FIPS module boundary.
Title Incorrect Tag Processing for Empty Messages in AES-GCM-SIV and AES-SIV modes
Weaknesses CWE-325
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
openssl
Published
Updated
Jun 10, 2026, 7:48 AM
Reserved
May 12, 2026, 2:34 PM
Status
Analyzed
Published
Jun 9, 2026, 5:17 PM
Modified
Jul 23, 2026, 8:10 AM
Severity
Low
Public date
Jun 9, 2026, 12:00 AM