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 products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| The Libreswan Project | libreswan | ≤ 5.3 | 5.3.1 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 13 | libreswan | No fix yet | — |
| Debian 12 | libreswan | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | libreswan | No fix yet | — |
| Ubuntu 26.04 LTS | libreswan | No fix yet | — |
| Ubuntu 25.10 | libreswan | No fix yet | — |
| Ubuntu 24.04 LTS | libreswan | No fix yet | — |
| Ubuntu 22.04 LTS | libreswan | No fix yet | — |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 20.04 LTS | libreswan | No fix yet | — |
| Ubuntu 18.04 LTS | libreswan | No fix yet | — |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 10 | libreswan +1 | 5.3.2-1.el10_2 | RHSA-2026:46398 |
| RHEL 9 | libreswan | 4.15-10.el9_8 | RHSA-2026:46986, RHSA-2026:46397 |
| RHEL 8 | libreswan | 4.12-2.el8_10.6 | RHSA-2026:46396 |
Show 10 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 10.0 EUS | libreswan | 5.2-1.el10_0.5 | RHSA-2026:55449 |
| RHEL 9.6 EUS | libreswan | 4.15-8.el9_6.1 | RHSA-2026:57741 |
| RHEL 9.4 E4S | libreswan | 4.12-3.el9_4.2 | RHSA-2026:61258 |
| RHEL 9.2 E4S | libreswan | 4.9-5.el9_2.5 | RHSA-2026:61779 |
| RHEL 8.8 TUS | libreswan | 4.9-3.el8_8.3 | RHSA-2026:72287 |
| RHEL 8.8 E4S | libreswan | 4.9-3.el8_8.3 | RHSA-2026:72287 |
| RHEL 8.6 EUS Long Life | libreswan | 4.5-1.el8_6.6 | RHSA-2026:82154 |
| RHEL 8.6 AUS | libreswan | 4.5-1.el8_6.6 | RHSA-2026:82154 |
| RHEL 8.4 EUS Long Life | libreswan | 4.3-6.el8_4.2 | RHSA-2026:84887 |
| RHEL 8.4 AUS | libreswan | 4.3-6.el8_4.2 | RHSA-2026:84887 |
AlmaLinux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux 10 | libreswan +1 | 5.3.2-1.el10_2 | ALSA-2026:46398 |
| AlmaLinux 9 | libreswan | 4.15-10.el9_8 | ALSA-2026:46397 |
| AlmaLinux 8 | libreswan | 4.12-2.el8_10.6 | ALSA-2026:46396 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 10 | libreswan | 5.3.2-1.el10_2 | RLSA-2026:46398 |
| Rocky Linux 9 | libreswan | 4.15-10.el9_8 | RLSA-2026:46397 |
| Rocky Linux 8 | libreswan | 4.12-2.el8_10.6 | RLSA-2026:46396 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | libreswan | 5.3.2-r0 | — |
| Alpine v3.23 | libreswan | 5.3.3-r0 | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | libreswan | 4.12-3.amzn2023.0.3 | ALAS2023-2026-2039 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | libreswan | 4.15-2 | — |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 10 | libreswan +1 | 5.3.2-1.el10_2 | ELSA-2026-46398 |
| Oracle Linux 9 | libreswan | 4.15-10.0.1.el9_8 | ELSA-2026-46397 |
| Oracle Linux 8 | libreswan | 4.12-2.0.1.el8_10.6 | ELSA-2026-46396 |
Advisories 23
- WID-SEC-2026-2518 Red Hat Enterprise Linux (libreswan): Mehrere Schwachstellen ermöglichen Denial of Service BSI CERT-Bund (WID) · Nov 1, 2026
- ALSA-2026:46397 Important: libreswan security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2026:46398 Important: libreswan security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2026:46396 Important: libreswan security update AlmaLinux Security Advisories · Oct 29, 2026
- RHSA-2026:84887 Red Hat Security Advisory: libreswan security update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- RHSA-2026:82154 Red Hat Security Advisory: libreswan security update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- RHSA-2026:72287 Red Hat Security Advisory: libreswan security update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- RHSA-2026:61779 Red Hat Security Advisory: libreswan security update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- RHSA-2026:61258 Red Hat Security Advisory: libreswan security update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- RHSA-2026:57741 Red Hat Security Advisory: libreswan security update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- RHSA-2026:55449 Red Hat Security Advisory: libreswan security update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- RHSA-2026:46986 Red Hat Security Advisory: libreswan security update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- RHSA-2026:46398 Red Hat Security Advisory: libreswan security update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- RHSA-2026:46397 Red Hat Security Advisory: libreswan security update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- RHSA-2026:46396 Red Hat Security Advisory: libreswan security update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- WID-SEC-2026-3043 IBM QRadar SIEM: Mehrere Schwachstellen BSI CERT-Bund (WID) · Sep 17, 2026
- ALAS2023-2026-2039 Important: libreswan security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Aug 4, 2026
- RLSA-2026:46398 Important: libreswan security update Rocky Linux Security Advisories · Jul 28, 2026
- RLSA-2026:46396 Important: libreswan security update Rocky Linux Security Advisories · Jul 28, 2026
- RLSA-2026:46397 Important: libreswan security update Rocky Linux Security Advisories · Jul 27, 2026
- ELSA-2026-46398 Important: libreswan security update (Oracle Linux 10) Oracle Linux Security Advisories (ELSA) · Jul 27, 2026
- ELSA-2026-46397 Important: libreswan security update (Oracle Linux 9) Oracle Linux Security Advisories (ELSA) · Jul 27, 2026
- ELSA-2026-46396 Important: libreswan security update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Jul 27, 2026
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