CVE-2026-50721
IKEv1 Denial of Service via RSA-SHA1 (PKCS#1 Version 1.5 Encrypted) authentication payload
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.
INFO
Published Date :
July 2, 2026, 10:16 p.m.
Last Modified :
July 9, 2026, 3:46 p.m.
Remotely Exploit :
Yes !
Source :
d42dc95b-23f1-4e06-9076-20753a0fb0df
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | d42dc95b-23f1-4e06-9076-20753a0fb0df | ||||
| CVSS 3.1 | HIGH | d42dc95b-23f1-4e06-9076-20753a0fb0df | ||||
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update Libreswan to the latest version.
- Verify signature verification logic.
- Monitor for impersonation attempts.
- Monitor for denial-of-service attacks.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-50721.
| URL | Resource |
|---|---|
| https://libreswan.org/security/CVE-2026-50721/ | Vendor Advisory |
| https://libreswan.org/security/CVE-2026-50721/CVE-2026-50721.txt | Vendor Advisory |
| https://libreswan.org/security/CVE-2026-50722/CVE-2026-50722.txt | Vendor Advisory |
| https://www.rfc-editor.org/rfc/rfc2313 | Technical Description |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-50721 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-50721
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-50721 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-50721 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Jul. 09, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Added CPE Configuration OR *cpe:2.3:a:libreswan:libreswan:*:*:*:*:*:*:*:* versions up to (excluding) 5.3.1 Added Reference Type Libreswan Project: https://libreswan.org/security/CVE-2026-50721/ Types: Vendor Advisory Added Reference Type Libreswan Project: https://libreswan.org/security/CVE-2026-50721/CVE-2026-50721.txt Types: Vendor Advisory Added Reference Type Libreswan Project: https://libreswan.org/security/CVE-2026-50722/CVE-2026-50722.txt Types: Vendor Advisory Added Reference Type Libreswan Project: https://www.rfc-editor.org/rfc/rfc2313 Types: Technical Description -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 07, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-50721', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-06T18:12:17.199605Z'} -
New CVE Received by d42dc95b-23f1-4e06-9076-20753a0fb0df
Jul. 02, 2026
Action Type Old Value New Value Added Affected [{'repo': 'https://github.com/libreswan/libreswan', 'vendor': 'The Libreswan Project', 'product': 'libreswan', 'versions': [{'status': 'affected', 'version': '0', 'versionType': 'semver', 'lessThanOrEqual': '5.3'}, {'status': 'unaffected', 'version': '5.3.1', 'versionType': 'semver'}], 'packageName': 'libreswan', 'collectionURL': 'https://github.com/libreswan/libreswan', 'defaultStatus': 'unaffected', 'programRoutines': [{'name': 'RSA_authenticate_hash_signature_raw_rsa'}]}] Added 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. Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H Added CWE CWE-347 Added CWE CWE-617 Added Reference https://libreswan.org/security/CVE-2026-50721/ Added Reference https://libreswan.org/security/CVE-2026-50721/CVE-2026-50721.txt Added Reference https://libreswan.org/security/CVE-2026-50722/CVE-2026-50722.txt Added Reference https://www.rfc-editor.org/rfc/rfc2313