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HIGH

CVE-2026-50721

CVSS v3

8.1

HIGH

EPSS Score

0.4 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • libreswanAlmaLinux:10all versions · fixed in 5.3.2-1.el10_2and 1 other package
  • libreswanAlmaLinux:9all versions · fixed in 4.15-10.el9_8
  • libreswanAlmaLinux:8all versions · fixed in 4.12-2.el8_10.6

Vendor advisories

  • CVE-2026-50721 Red Hat Product Security101 products fixed · 3 known affected

    librenswan: IKEv1 Denial of Service via RSA-SHA1 (PKCS#1 Version 1.5 Encrypted) authentication payload

    libreswan.src as a component of Red Hat Enterprise Linux 6 · libreswan as a component of Red Hat Enterprise Linux 7 · libreswan.src as a component of Red Hat Enterprise Linux 7

  • RHSA-2026:84887 Red Hat Product Security4 products fixed

    Red Hat Security Advisory: libreswan security update

  • RHSA-2026:82154 Red Hat Product Security4 products fixed

    Red Hat Security Advisory: libreswan security update

  • RHSA-2026:72287 Red Hat Product Security5 products fixed

    Red Hat Security Advisory: libreswan security update

  • RHSA-2026:63044 Red Hat Product Security4 products fixed

    Red Hat Security Advisory: OpenShift Container Platform 4.19.46 bug fix and security update

  • RHSA-2026:63041 Red Hat Product Security4 products fixed

    Red Hat Security Advisory: OpenShift Container Platform 4.21.32 bug fix and security update

9 more advisories

Full record on NVD

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.

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Published
2026-07-02
Last Modified
2026-07-02

Frequently asked questions

What is CVE-2026-50721?

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.

Is CVE-2026-50721 actively exploited?

Active exploitation of CVE-2026-50721 has not been confirmed. Its EPSS score was 0.4% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-50721?

CVE-2026-50721 has a CVSS v3 base score of 8.1 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.

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