Libreswan < 5.3.1 Multiple Vulnerabilities

medium Nessus Plugin ID 327415

Synopsis

The version of Libreswan installed on the remote host is affected by multiple vulnerabilities.

Description

The version of Libreswan installed on the remote host is prior to 5.3.1. It is, therefore, affected by multiple vulnerabilities:

- 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. (CVE-2026-50721)

- 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. (CVE-2026-50722)

Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Solution

Upgrade to Libreswan version 5.3.1 or later.

Plugin Details

Severity: Medium

ID: 327415

File Name: libreswan_CVE-2026-50721.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Misc.

Published: 7/16/2026

Updated: 7/16/2026

Supported Sensors: Nessus Agent, Nessus

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.8

CVSS v2

Risk Factor: Medium

Base Score: 5.4

Vector: CVSS2#AV:N/AC:H/Au:N/C:N/I:N/A:C

CVSS Score Source: CVE-2026-50721

CVSS v3

Risk Factor: Medium

Base Score: 5.9

Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Vulnerability Information

CPE: cpe:/a:libreswan:libreswan

Required KB Items: installed_sw/Libreswan

Patch Publication Date: 6/24/2026

Vulnerability Publication Date: 6/24/2026

Reference Information

CVE: CVE-2026-50721, CVE-2026-50722

Detections

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