CVE-2026-50721

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.

CVSS 3.1

5.9CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

0.4% chance of exploitation in the next 30 days; higher than 32% of CVEs (scores of 2026-10-25)

CWEs

CWE-347, CWE-617

Published

2026-07-02

Modified

2026-10-25

Record from

the NVD, synced 2026-10-25

Affected

• libreswan:libreswan

References

• https://libreswan.org/security/CVE-2026-50721/
• https://libreswan.org/security/CVE-2026-50721/CVE-2026-50721.txt
• https://libreswan.org/security/CVE-2026-50722/CVE-2026-50722.txt
• https://www.rfc-editor.org/rfc/rfc2313

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