libreswan up to 5.3.0 X.509 Certificate RSA_authenticate_hash_signature_pkcs1_1_5_rsa Bleichenbacher signature verification

Summaryinfo

A vulnerability was found in libreswan up to 5.3.0 and classified as problematic. This vulnerability affects the function RSA_authenticate_hash_signature_pkcs1_1_5_rsa of the component X.509 Certificate Handler. Such manipulation leads to signature verification. This vulnerability is documented as CVE-2026-50722. The attack can be executed remotely. There is not any exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in libreswan up to 5.3.0 and classified as problematic. Affected by this issue is the function RSA_authenticate_hash_signature_pkcs1_1_5_rsa of the component X.509 Certificate Handler. The manipulation with an unknown input leads to a signature verification vulnerability. Using CWE to declare the problem leads to CWE-347. The product does not verify, or incorrectly verifies, the cryptographic signature for data. Impacted is confidentiality, integrity, and availability. CVE summarizes:

Libreswan, via the function RSA_authenticate_hash_signature_pkcs1_1_5_rsa(), did not correctly verify the DER encoding of the ASN.1 digest when the IKEv2 AUTH payload was encoded using RSASSA-PKCS1-v1_5 (RFC 8017). A remote attacker can use a variation on the Bleichenbacher attack to forge the AUTH payload when small public exponents are used (e.g., e=3), leading to impersonation. Additionally, a remote attacker, by encoding a shorter than expected hash in the AUTH 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 the remote IKE peer are not affected.

The weakness was released by Yeonghyeon Choi and Duyeong Kim. The advisory is shared for download at libreswan.org. This vulnerability is handled as CVE-2026-50722 since 06/05/2026. The exploitation is known to be difficult. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available.

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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