Vulnerability · Published Jul 2, 2026 · Assigned by libreswan
CVE-2026-50721IKEv1 Denial of Service via RSA-SHA1 (PKCS#1 Version 1.5 Encrypted) authentication payload
High 7.5
In plain English
A high-severity security flaw in libreswan from The Libreswan Project. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 33% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | libreswan | 5.3.2-1.el10_2 | ALSA-2026:46398 |
| AlmaLinux:8 | libreswan | 4.12-2.el8_10.6 | ALSA-2026:46396 |
| AlmaLinux:9 | libreswan | 4.15-10.el9_8 | ALSA-2026:46397 |
| AlmaLinux:10 | libreswan-minimal | 5.3.2-1.el10_2 | ALSA-2026:46398 |
| Alpine:v3.23 | libreswan | 5.3.3-r0 | ALPINE-CVE-2026-50721 |
| Alpine:v3.24 | libreswan | 5.3.2-r0 | ALPINE-CVE-2026-50721 |
| Debian:12 | libreswan | no fix listed | DEBIAN-CVE-2026-50721 |
| Debian:13 | libreswan | no fix listed | DEBIAN-CVE-2026-50721 |
| Rocky Linux:10 | libreswan | 0:5.3.2-1.el10_2 | RLSA-2026:46398 |
| Rocky Linux:8 | libreswan | 0:4.12-2.el8_10.6 | RLSA-2026:46396 |
| Rocky Linux:9 | libreswan | 0:4.15-10.el9_8 | RLSA-2026:46397 |
| Ubuntu:22.04:LTS | libreswan | no fix listed | UBUNTU-CVE-2026-50721 |
| Ubuntu:24.04:LTS | libreswan | no fix listed | UBUNTU-CVE-2026-50721 |
| Ubuntu:25.10 | libreswan | no fix listed | UBUNTU-CVE-2026-50721 |
| Ubuntu:26.04:LTS | libreswan | no fix listed | UBUNTU-CVE-2026-50721 |
| Ubuntu:26.10 | libreswan | no fix listed | UBUNTU-CVE-2026-50721 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| The Libreswan Project | libreswan | 0 – through 5.3 |
Weakness: CWE-347, CWE-617 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- Libreswan Security Advisory CVE-2026-50721 vendor-advisory
- Libreswan CVE-2026-50721 Patches patch
- Related: CVE-2026-50722 (IKEv2 variant) related
- RFC 2313 - PKCS #1: RSA Encryption Version 1.5 technical-description