CVE-2026-50721 Affecting libreswan package, versions <5.2-2.5


Severity

Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.39% (32nd percentile)

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  • Snyk IDSNYK-DEBIANUNSTABLE-LIBRESWAN-17808257
  • published3 Jul 2026
  • disclosed2 Jul 2026

Introduced: 2 Jul 2026

CVE-2026-50721  (opens in a new tab)

How to fix?

Upgrade Debian:unstable libreswan to version 5.2-2.5 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream libreswan package and not the libreswan package as distributed by Debian. See How to fix? for Debian:unstable relevant fixed versions and status.

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 Base Scores

version 3.1