CVE-2026-50722
IKEv2 Denial of Service via RSA-SHA1 (PKCS#1 RSASSA-PKCS1-v1_5) authentication payload
- Published
- Updated
- Reserved
- Assigned by
- libreswan
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| libreswanCNA (assigner) | 3.1 | High7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| libreswanCNA (assigner) | 3.1 | High8.1 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H |
| NVDNVD · Analyzed | 3.1 | Medium5.9 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 0.35% · top 72% of all CVEs (7 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: yes · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.5.
Weakness
Affected products
The Libreswan Project · libreswan
- affected ≤ 5.3
- unaffected 5.3.1
What to do
Solution: Upgrade to libreswan 5.3.1 or later. Patches for libreswan 4.15 and 5.3 are available at https://libreswan.org/security/CVE-2026-50722/
Workaround: If Windows support is not needed, configure authby=ecdsa or authby=rsa-sha2 (or both via authby=ecdsa,rsa-sha2) to disallow the fallback of RSA PKCS#1 1.5. The leftauth= and rightauth= settings can be updated similarly if those are in use instead of authby.
Exploitation: No known exploitation in the wild. The authentication bypass requires the target to use RSA keys with weak exponents (e=3), which have been disallowed by most cryptographic libraries for at least a decade. The denial-of-service attack is exploitable against any IKEv2 configuration using default authby= settings that permit RSA PKCS#1 v1.5 fallback.
References (4)
- Libreswan Security Advisory CVE-2026-50722 (opens in a new tab)vendor-advisory
- Libreswan CVE-2026-50722 Patches (opens in a new tab)patch
- Related: CVE-2026-50721 (IKEv1 variant) (opens in a new tab)related
- RFC 8017 - PKCS #1: RSA Cryptography Specifications Version 2.2 (opens in a new tab)technical-description
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-50722)Record last updated .