libreswan up to 5.3.0 X.509 Certificate RSA_authenticate_hash_signature_raw_rsa Bleichenbacher signature verification

Summaryinfo

A vulnerability has been found in libreswan up to 5.3.0 and classified as problematic. This affects the function RSA_authenticate_hash_signature_raw_rsa of the component X.509 Certificate Handler. This manipulation causes signature verification. This vulnerability is registered as CVE-2026-50721. Remote exploitation of the attack is possible. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability has been found in libreswan up to 5.3.0 and classified as problematic. Affected by this vulnerability is the function RSA_authenticate_hash_signature_raw_rsa of the component X.509 Certificate Handler. The manipulation with an unknown input leads to a signature verification vulnerability. The CWE definition for the vulnerability is CWE-347. The product does not verify, or incorrectly verifies, the cryptographic signature for data. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

Libreswan, via the function RSA_authenticate_hash_signature_raw_rsa(), did not correctly verify the length of the authentication hash when the SIG payload of an IKEv1 packet was encoded using PKCS #1 RSA Encryption as per RFC 2313. A remote attacker can use a variation on the Bleichenbacher attack to forge the SIG payload when small public exponents are being used (e.g., e=3), which could lead to impersonation. Additionally, a remote attacker, by encoding a shorter than expected hash in the SIG payload, could trigger an assertion leading to denial-of-service. The daemon aborts and restarts; continued exploitation causes sustained denial of service. Remote code execution is not possible. X.509 certificate verifications of remote IKE peers are not affected.

The weakness was published by Yeonghyeon Choi and Duyeong Kim. It is possible to read the advisory at libreswan.org. This vulnerability is known as CVE-2026-50721 since 06/05/2026. The exploitation appears to be difficult. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 5.3.1 eliminates this vulnerability.

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Productinfo

Name

• libreswan

Version

• 5.0
• 5.1
• 5.2
• 5.3.0

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