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

Vulnerability from cvelistv5 – Published: 2026-07-02 21:44 – Updated: 2026-07-02 21:44
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
CWE
  • CWE-347 - Improper Verification of Cryptographic Signature
  • CWE-617 - Reachable Assertion
Assigner
References
Impacted products
Vendor Product Version
The Libreswan Project libreswan Affected: 0 , ≤ 5.3 (semver)
Unaffected: 5.3.1 (semver)
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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          "defaultStatus": "unaffected",
          "packageName": "libreswan",
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          "programRoutines": [
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          "vendor": "The Libreswan Project",
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              "status": "affected",
              "version": "0",
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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."
        }
      ],
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          "type": "finder",
          "value": "Yeonghyeon Choi"
        },
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          "lang": "en",
          "type": "finder",
          "value": "Duyeong Kim"
        },
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          "type": "analyst",
          "value": "Andrew Cagney (The Libreswan Team)"
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              "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"
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          "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."
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          "descriptions": [
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              "lang": "en",
              "value": "Denial of Service via assertion failure in pluto daemon when processing malformed RSA PKCS#1 v1.5 SIG payloads in IKEv1"
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        {
          "capecId": "CAPEC-473",
          "descriptions": [
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              "lang": "en",
              "value": "Authentication bypass via Bleichenbacher-style signature forgery when weak RSA exponents (e.g., e=3) are in use"
            }
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            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
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        "shortName": "libreswan"
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        },
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          "name": "Libreswan CVE-2026-50721 Patches",
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          "url": "https://libreswan.org/security/CVE-2026-50721/"
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        {
          "name": "Related: CVE-2026-50722 (IKEv2 variant)",
          "tags": [
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          ],
          "url": "https://libreswan.org/security/CVE-2026-50722/CVE-2026-50722.txt"
        },
        {
          "name": "RFC 2313 - PKCS #1: RSA Encryption Version 1.5",
          "tags": [
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      "solutions": [
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              "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"
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      "timeline": [
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          "lang": "en",
          "time": "2026-03-24T00:00:00.000Z",
          "value": "Libreswan notified of the issue via security@libreswan.org"
        },
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          "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"
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      "title": "IKEv1 Denial of Service via RSA-SHA1 (PKCS#1 Version 1.5 Encrypted) authentication payload",
      "workarounds": [
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              "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."
        }
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    "datePublished": "2026-07-02T21:44:09.423Z",
    "dateReserved": "2026-06-05T16:10:05.751Z",
    "dateUpdated": "2026-07-02T21:44:09.423Z",
    "state": "PUBLISHED"
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  }
}


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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

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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.


Detection rules are retrieved from Rulezet.