CVE-2026-50721 (GCVE-0-2026-50721)

Vulnerability from cvelistv5 – Published: 2026-07-02 21:44 – Updated: 2026-07-07 17:01
VLAI
Title
IKEv1 Denial of Service via RSA-SHA1 (PKCS#1 Version 1.5 Encrypted) authentication payload
Summary
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.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.1 (High)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-06 18:12 UTC
CWE
  • CWE-347 - Improper Verification of Cryptographic Signature
  • CWE-617 - Reachable Assertion
Assigner
References
Impacted products
Vendor Product Version CPE status
The Libreswan Project libreswan Affected: 0 , ≤ 5.3 (semver)
Unaffected: 5.3.1 (semver)
guessed Create a notification for this product.
Credits
Yeonghyeon Choi Duyeong Kim Andrew Cagney (The Libreswan Team)
Show details on NVD website
To clipboard 

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              "value": "Any server or client that accepts RSA-based IKEv1 connections via the default authby=rsasig option is vulnerable to denial of service. Authentication bypass additionally requires the use of RSA keys with weak exponents (e=3). IKEv1 only supports RSA-SHA1 (PKCS#1 Version 1.5) for public key authentication, so the vulnerable code path cannot be disabled without migrating to IKEv2 or switching to PSK."
            }
          ],
          "credits": [
            {
              "lang": "en",
              "type": "finder",
              "value": "Yeonghyeon Choi"
            },
            {
              "lang": "en",
              "type": "finder",
              "value": "Duyeong Kim"
            },
            {
              "lang": "en",
              "type": "analyst",
              "value": "Andrew Cagney (The Libreswan Team)"
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "supportingMedia": [
                {
                  "base64": false,
                  "type": "text/html",
                  "value": "\u003cp\u003eLibreswan, 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.\u003c/p\u003e"
                }
              ],
              "value": "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."
            }
          ],
          "exploits": [
            {
              "lang": "en",
              "value": "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 IKEv1 configuration using the default authby=rsasig option."
            }
          ],
          "impacts": [
            {
              "capecId": "CAPEC-463",
              "descriptions": [
                {
                  "lang": "en",
                  "value": "Denial of Service via assertion failure in pluto daemon when processing malformed RSA PKCS#1 v1.5 SIG payloads in IKEv1"
                }
              ]
            },
            {
              "capecId": "CAPEC-473",
              "descriptions": [
                {
                  "lang": "en",
                  "value": "Authentication bypass via Bleichenbacher-style signature forgery when weak RSA exponents (e.g., e=3) are in use"
                }
              ]
            }
          ],
          "metrics": [
            {
              "cvssV3_1": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 7.5,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "NONE",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
                "version": "3.1"
              },
              "format": "CVSS",
              "scenarios": [
                {
                  "lang": "en",
                  "value": "GENERAL"
                }
              ]
            },
            {
              "cvssV3_1": {
                "attackComplexity": "HIGH",
                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 8.1,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "format": "CVSS",
              "scenarios": [
                {
                  "lang": "en",
                  "value": "Weak RSA exponent (e=3) in use, enabling Bleichenbacher signature forgery"
                }
              ]
            },
            {
              "other": {
                "content": {
                  "description": "Vendor-assessed severity: Medium. Authentication bypass requires weak RSA exponents (e=3) which have been disallowed by most cryptographic libraries for over a decade. DoS is mitigated by automatic daemon restart.",
                  "value": "MEDIUM"
                },
                "type": "vendorSeverity"
              }
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-347",
                  "description": "CWE-347: Improper Verification of Cryptographic Signature",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            },
            {
              "descriptions": [
                {
                  "cweId": "CWE-617",
                  "description": "CWE-617: Reachable Assertion",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-07-02T21:44:09.423Z",
            "orgId": "d42dc95b-23f1-4e06-9076-20753a0fb0df",
            "shortName": "libreswan"
          },
          "references": [
            {
              "name": "Libreswan Security Advisory CVE-2026-50721",
              "tags": [
                "vendor-advisory"
              ],
              "url": "https://libreswan.org/security/CVE-2026-50721/CVE-2026-50721.txt"
            },
            {
              "name": "Libreswan CVE-2026-50721 Patches",
              "tags": [
                "patch"
              ],
              "url": "https://libreswan.org/security/CVE-2026-50721/"
            },
            {
              "name": "Related: CVE-2026-50722 (IKEv2 variant)",
              "tags": [
                "related"
              ],
              "url": "https://libreswan.org/security/CVE-2026-50722/CVE-2026-50722.txt"
            },
            {
              "name": "RFC 2313 - PKCS #1: RSA Encryption Version 1.5",
              "tags": [
                "technical-description"
              ],
              "url": "https://www.rfc-editor.org/rfc/rfc2313"
            }
          ],
          "solutions": [
            {
              "lang": "en",
              "supportingMedia": [
                {
                  "base64": false,
                  "type": "text/html",
                  "value": "\u003cp\u003eUpgrade to libreswan 5.3.1 or later. Patches for libreswan 4.15 and 5.3 are available at \u003ca href=\"https://libreswan.org/security/CVE-2026-50721/\"\u003ehttps://libreswan.org/security/CVE-2026-50721/\u003c/a\u003e\u003c/p\u003e"
                }
              ],
              "value": "Upgrade to libreswan 5.3.1 or later. Patches for libreswan 4.15 and 5.3 are available at https://libreswan.org/security/CVE-2026-50721/"
            }
          ],
          "source": {
            "defects": [
              "CVE-2026-50721"
            ],
            "discovery": "EXTERNAL"
          },
          "taxonomyMappings": [
            {
              "taxonomyName": "ATT\u0026CK",
              "taxonomyRelations": [
                {
                  "relationshipName": "maps to",
                  "relationshipValue": "Application or System Exploitation (DoS)",
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              "taxonomyVersion": "15.1"
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          ],
          "timeline": [
            {
              "lang": "en",
              "time": "2026-03-24T00:00:00.000Z",
              "value": "Libreswan notified of the issue via security@libreswan.org"
            },
            {
              "lang": "en",
              "time": "2026-06-16T00:00:00.000Z",
              "value": "Advanced notice given to supported customers and distributions"
            },
            {
              "lang": "en",
              "time": "2026-06-24T00:00:00.000Z",
              "value": "Public announcement and release of libreswan 5.3.1"
            }
          ],
          "title": "IKEv1 Denial of Service via RSA-SHA1 (PKCS#1 Version 1.5 Encrypted) authentication payload",
          "workarounds": [
            {
              "lang": "en",
              "supportingMedia": [
                {
                  "base64": false,
                  "type": "text/html",
                  "value": "\u003cp\u003eIKEv1 only supports RSA-SHA1 (PKCS#1 Version 1.5) with public key authentication, so there is no way to disable the vulnerable code path within IKEv1. Migrate IKEv1 connections to IKEv2 where \u003ccode\u003eauthby=ecdsa\u003c/code\u003e or \u003ccode\u003eauthby=rsa-sha2\u003c/code\u003e can be configured. For static tunnel configurations (not Remote Access VPN Client groups), authentication can be changed to use PSK via \u003ccode\u003eauthby=secret\u003c/code\u003e after coordination with the remote peer.\u003c/p\u003e"
                }
              ],
              "value": "IKEv1 only supports RSA-SHA1 (PKCS#1 Version 1.5) with public key authentication, so there is no way to disable the vulnerable code path within IKEv1. Migrate IKEv1 connections to IKEv2 where authby=ecdsa or authby=rsa-sha2 can be configured. For static tunnel configurations (not Remote Access VPN Client groups), authentication can be changed to use PSK via authby=secret after coordination with the remote peer."
            }
          ],
          "x_generator": {
            "engine": "cvelib 1.8.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "d42dc95b-23f1-4e06-9076-20753a0fb0df",
        "assignerShortName": "libreswan",
        "cveId": "CVE-2026-50721",
        "datePublished": "2026-07-02T21:44:09.423Z",
        "dateReserved": "2026-06-05T16:10:05.751Z",
        "dateUpdated": "2026-07-07T17:01:58.011Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.