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 (v2.0.3)
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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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.\"}}}], \"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\"}]}], \"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.\"}], \"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\"}], \"solutions\": [{\"lang\": \"en\", \"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/\", \"supportingMedia\": [{\"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\", \"base64\": false}]}], \"references\": [{\"url\": \"https://libreswan.org/security/CVE-2026-50721/CVE-2026-50721.txt\", \"name\": \"Libreswan Security Advisory CVE-2026-50721\", \"tags\": [\"vendor-advisory\"]}, {\"url\": \"https://libreswan.org/security/CVE-2026-50721/\", \"name\": \"Libreswan CVE-2026-50721 Patches\", \"tags\": [\"patch\"]}, {\"url\": \"https://libreswan.org/security/CVE-2026-50722/CVE-2026-50722.txt\", \"name\": \"Related: CVE-2026-50722 (IKEv2 variant)\", \"tags\": [\"related\"]}, {\"url\": \"https://www.rfc-editor.org/rfc/rfc2313\", \"name\": \"RFC 2313 - PKCS #1: RSA Encryption Version 1.5\", \"tags\": [\"technical-description\"]}], \"workarounds\": [{\"lang\": \"en\", \"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.\", \"supportingMedia\": [{\"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\", \"base64\": false}]}], \"x_generator\": {\"engine\": \"cvelib 1.8.0\"}, \"descriptions\": [{\"lang\": \"en\", \"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.\", \"supportingMedia\": [{\"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\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-347\", \"description\": \"CWE-347: Improper Verification of Cryptographic Signature\"}]}, {\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-617\", \"description\": \"CWE-617: Reachable Assertion\"}]}], \"configurations\": [{\"lang\": \"en\", \"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.\"}], \"providerMetadata\": {\"orgId\": \"d42dc95b-23f1-4e06-9076-20753a0fb0df\", \"shortName\": \"libreswan\", \"dateUpdated\": \"2026-07-02T21:44:09.423Z\"}, \"taxonomyMappings\": [{\"taxonomyName\": \"ATT\u0026CK\", \"taxonomyVersion\": \"15.1\", \"taxonomyRelations\": [{\"taxonomyId\": \"T1499.004\", \"relationshipName\": \"maps to\", \"relationshipValue\": \"Application or System Exploitation (DoS)\"}]}]}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-50721\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-07-07T17:01:58.011Z\", \"dateReserved\": \"2026-06-05T16:10:05.751Z\", \"assignerOrgId\": \"d42dc95b-23f1-4e06-9076-20753a0fb0df\", \"datePublished\": \"2026-07-02T21:44:09.423Z\", \"assignerShortName\": \"libreswan\"}",
      "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.


Detection rules are retrieved from Rulezet.