Vulnerability in Libreswan
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.004 (30.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 31st percentile — 30.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000
Affected products
- Libreswan
- The Libreswan Project — versions 0, 5.3.1
Weakness classification (CWE)
References
- d42dc95b-23f1-4e06-9076-20753a0fb0df (vendor-advisory, Vendor Advisory)
- d42dc95b-23f1-4e06-9076-20753a0fb0df (patch, Vendor Advisory)
- d42dc95b-23f1-4e06-9076-20753a0fb0df (related, Vendor Advisory)
- d42dc95b-23f1-4e06-9076-20753a0fb0df (Technical Description, technical-description)
Frequently asked questions
- What is CVE-2026-50721?
- CVE-2026-50721 is a high-severity vulnerability in Libreswan, classified under Improper Verification of Cryptographic Signature. CVSS score: 8.1/10. Published 2026-07-02.
- How severe is CVE-2026-50721?
- High severity. CVSS v3 base score is 8.1 out of 10.