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Fencer Intel
high 8.1

CVE-2026-50721 json

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

published 4mo ago modified 17d ago also EUVD-2026-41441

cvss
8.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 33%
public exploits
0
none known

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.

Patch / fix

  • The Libreswan Project libreswan 5.3.1
  • libreswan RHEL 9 5.3.2-1.el9fdp
  • libreswan RHEL 10.2 5.3.2-1.el10_2
  • libreswan-minimal RHEL 10.2 5.3.2-1.el10_2
  • libreswan RHEL 8 4.12-2.el8_10.6
  • libreswan RHEL 9 4.15-10.el9_8
  • libreswan RHEL 8.4 EUS_LONG_LIFE, RHEL 8.4 AUS 4.3-6.el8_4.2
  • libreswan RHEL 8.6 EUS_LONG_LIFE, RHEL 8.6 AUS 4.5-1.el8_6.6
  • libreswan RHEL 8.8 TUS, RHEL 8.8 E4S 4.9-3.el8_8.3

red hat advisories RHSA-2026:84887RHSA-2026:82154RHSA-2026:72287RHSA-2026:61779RHSA-2026:61258RHSA-2026:57741

  • libreswan AlmaLinux 8 4.12-2.el8_10.6
  • libreswan AlmaLinux 9 4.15-10.el9_8
  • libreswan AlmaLinux 10 5.3.2-1.el10_2
  • libreswan-minimal AlmaLinux 10 5.3.2-1.el10_2

almalinux advisories ALSA-2026:46396ALSA-2026:46397ALSA-2026:46398

  • libreswan Rocky Linux 10 5.3.2-1.el10_2
  • libreswan Rocky Linux 8 4.12-2.el8_10.6
  • libreswan Rocky Linux 9 4.15-10.el9_8

rocky linux advisories RLSA-2026:46398RLSA-2026:46396RLSA-2026:46397

  • libreswan Alpine 3.23 5.3.3-r0
  • libreswan Alpine 3.24 5.3.2-r0

alpine advisories ALPINE-CVE-2026-50721

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • libreswan Azure Linux 3.0 4.15-2

azure linux advisories AZL-91773

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Is CVE-2026-50721 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-50721 updated cvss 7.5

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

  • Red Hat Enterprise Linux 6 libreswan
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 libreswan Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: workaround, no fix available
  • Red Hat Fast Datapath for Red Hat Enterprise Linux 9 libreswan 5.3.2-1.el9fdp
    fixed: vendor fix RHSA-2026:46986
  • Red Hat Enterprise Linux AppStream (v. 8) libreswan 4.12-2.el8_10.6
    fixed: vendor fix RHSA-2026:46396
  • Red Hat Enterprise Linux AppStream (v. 9) libreswan 4.15-10.el9_8
    fixed: vendor fix RHSA-2026:46397
  • Red Hat Enterprise Linux AppStream (v. 10) libreswan 5.3.2-1.el10_2, libreswan-minimal 5.3.2-1.el10_2
    fixed: vendor fix RHSA-2026:46398
  • Red Hat Enterprise Linux AppStream AUS (v.8.4) libreswan 4.3-6.el8_4.2
    fixed: vendor fix RHSA-2026:84887
  • Red Hat Enterprise Linux AppStream AUS (v.8.6) libreswan 4.5-1.el8_6.6
    fixed: vendor fix RHSA-2026:82154
show 12 more
  • Red Hat Enterprise Linux AppStream E4S (v.8.8) libreswan 4.9-3.el8_8.3
    fixed: vendor fix RHSA-2026:72287
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) libreswan 4.9-5.el9_2.5
    fixed: vendor fix RHSA-2026:61779
  • Red Hat Enterprise Linux AppStream E4S (v.9.4) libreswan 4.12-3.el9_4.2
    fixed: vendor fix RHSA-2026:61258
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) libreswan 5.2-1.el10_0.5
    fixed: vendor fix RHSA-2026:55449
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) libreswan 4.15-8.el9_6.1
    fixed: vendor fix RHSA-2026:57741
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.4) libreswan 4.3-6.el8_4.2
    fixed: vendor fix RHSA-2026:84887
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.6) libreswan 4.5-1.el8_6.6
    fixed: vendor fix RHSA-2026:82154
  • Red Hat Enterprise Linux AppStream TUS (v.8.8) libreswan 4.9-3.el8_8.3
    fixed: vendor fix RHSA-2026:72287
  • Red Hat OpenShift Container Platform 4.19 rhcos 4.19.9.6.202609021231
    fixed: vendor fix RHSA-2026:63044
  • Red Hat OpenShift Container Platform 4.20 rhcos 4.20.9.6.202609021029
    fixed: vendor fix RHSA-2026:63100
  • Red Hat OpenShift Container Platform 4.21 rhcos 4.21.9.6.202609021100
    fixed: vendor fix RHSA-2026:63041
  • Red Hat Enterprise Linux AppStream AUS (v.8.4) libreswan-debuginfo 4.3-6.el8_4.2, libreswan-debugsource 4.3-6.el8_4.2 Red Hat Enterprise Linux AppStream AUS (v.8.6) libreswan-debuginfo 4.5-1.el8_6.6, libreswan-debugsource 4.5-1.el8_6.6 Red Hat Enterprise Linux AppStream E4S (v.8.8) libreswan-debuginfo 4.9-3.el8_8.3, libreswan-debugsource 4.9-3.el8_8.3 Red Hat Enterprise Linux AppStream E4S (v.9.2) libreswan-debuginfo 4.9-5.el9_2.5, libreswan-debugsource 4.9-5.el9_2.5 Red Hat Enterprise Linux AppStream E4S (v.9.4) libreswan-debuginfo 4.12-3.el9_4.2, libreswan-debugsource 4.12-3.el9_4.2 Red Hat Enterprise Linux AppStream EUS (v. 10.0) libreswan-debuginfo 5.2-1.el10_0.5, libreswan-debugsource 5.2-1.el10_0.5
    +5 more products
    Red Hat Enterprise Linux AppStream EUS (v.9.6) libreswan-debuginfo 4.15-8.el9_6.1, libreswan-debugsource 4.15-8.el9_6.1 Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.4) libreswan-debuginfo 4.3-6.el8_4.2, libreswan-debugsource 4.3-6.el8_4.2 Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.6) libreswan-debuginfo 4.5-1.el8_6.6, libreswan-debugsource 4.5-1.el8_6.6 Red Hat Enterprise Linux AppStream TUS (v.8.8) libreswan-debuginfo 4.9-3.el8_8.3, libreswan-debugsource 4.9-3.el8_8.3 Red Hat OpenShift Container Platform 4 libreswan
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
4mo ago

Exploit prediction

0.39% chance of exploitation in the next 30 days, higher than 33% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • The Libreswan Project libreswan

Classification

Weakness
  • CWE-347 Improper Verification of Cryptographic Signature
  • CWE-617 Reachable Assertion

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.