Vulnerability Description
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 Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Libreswan | Libreswan | < 5.3.1 |
Related Weaknesses (CWE)
References
- https://libreswan.org/security/CVE-2026-50721/Vendor Advisory
- https://libreswan.org/security/CVE-2026-50721/CVE-2026-50721.txtVendor Advisory
- https://libreswan.org/security/CVE-2026-50722/CVE-2026-50722.txtVendor Advisory
- https://www.rfc-editor.org/rfc/rfc2313Technical Description
FAQ
What is CVE-2026-50721?
CVE-2026-50721 is a vulnerability with a CVSS score of 8.1 (HIGH). 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 ...
How severe is CVE-2026-50721?
CVE-2026-50721 has been rated HIGH with a CVSS base score of 8.1/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-50721?
Check the references section above for vendor advisories and patch information. Affected products include: Libreswan Libreswan.