What’s Vulnerable › Vulnerabilities

CVE-2026-50722: IKEv2 Denial of Service via RSA-SHA1 (PKCS#1 RSASSA-PKCS1-v1_5) authentication payload

• Severity: medium (CVSS 5.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-02 · updated 2026-10-25
• Weakness: CWE-347

Description

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.

Affected products

• The Libreswan Project libreswan: before 5.3.1 — fixed in 5.3.1

How to fix

Upgrade to a fixed version: The Libreswan Project libreswan 5.3.1. Check the vendor advisory for mitigations.

References

• https://libreswan.org/security/CVE-2026-50721/CVE-2026-50721.txt
• https://libreswan.org/security/CVE-2026-50722/
• https://libreswan.org/security/CVE-2026-50722/CVE-2026-50722.txt
• https://www.rfc-editor.org/rfc/rfc8017

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