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Fencer Vulns
medium 5.9

CVE-2026-40356 json

In MIT Kerberos 5 (aka krb5) before 1.22.3, there is an integer underflow and resultant out-of...

published 2026-04-28 6 mo ago modified 2026-10-26 13 d ago also EUVD-2026-25993 , GHSA-f7p3-6rhj-p7jv , JLSEC-2026-1259

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 49%
public exploits
0
none known

Summary

In MIT Kerberos 5 (aka krb5) before 1.22.3, there is an integer underflow and resultant out-of-bounds read if an application calls gss_accept_sec_context() on a system with a NegoEx mechanism registered in /etc/gss/mech. An unauthenticated remote attacker can trigger this, possibly causing the process to terminate in parse_message.

Patch / fix

  • MIT Kerberos 5 1.22.3
  • krb5 Debian 12 1.20.1-2+deb12u5
  • krb5 Debian 13 1.21.3-5+deb13u1
  • krb5 Debian 14 1.22.1-2.1

debian advisories DEBIAN-CVE-2026-40356

  • krb5 Ubuntu 22.04 LTS 1.19.2-2ubuntu0.8
  • krb5 Ubuntu 24.04 LTS 1.20.1-6ubuntu2.7
  • krb5 Ubuntu 26.04 LTS 1.22.1-2ubuntu4.1

ubuntu advisories UBUNTU-CVE-2026-40356

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • krb5 RHEL 9 1.21.1-10.el9_8
  • libkadm5 RHEL 9 1.21.1-10.el9_8
  • krb5-libs RHEL 9 1.21.1-10.el9_8
  • krb5-pkinit RHEL 9 1.21.1-10.el9_8
  • krb5-server RHEL 9 1.21.1-10.el9_8
  • krb5-server-ldap RHEL 9 1.21.1-10.el9_8
  • krb5-workstation RHEL 9 1.21.1-10.el9_8
  • krb5-xrealmauthz RHEL 9 1.21.1-10.el9_8

red hat advisories RHSA-2026:24686RHSA-2026:24683RHSA-2026:24685RHSA-2026:19357RHSA-2026:19145RHSA-2026:16799

  • krb5 SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Server Applications 15 SP7 +1 more 1.20.1-150600.11.19.1
  • krb5 SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 1.21.3-160000.3.1
  • krb5 SLE Micro 5.4, SLE Micro 5.3 1.19.2-150400.3.21.1

suse advisories SUSE-SU-2026:2848-1SUSE-SU-2026:22255-1SUSE-SU-2026:22322-1SUSE-SU-2026:2449-1

  • krb5 openSUSE Leap 16.0 1.21.3-160000.3.1
  • krb5 openSUSE Tumbleweed 1.22.2-3.1

opensuse advisories openSUSE-SU-2026:21021-1openSUSE-SU-2026:10729-1

  • libkadm5 AlmaLinux 10 1.21.3-10.el10_2
  • krb5-libs AlmaLinux 10 1.21.3-10.el10_2
  • krb5-pkinit AlmaLinux 10 1.21.3-10.el10_2
  • krb5-server AlmaLinux 10 1.21.3-10.el10_2
  • krb5-server-ldap AlmaLinux 10 1.21.3-10.el10_2
  • krb5-workstation AlmaLinux 10 1.21.3-10.el10_2
  • krb5-xrealmauthz AlmaLinux 10 1.21.3-10.el10_2
  • libkadm5 AlmaLinux 9 1.21.1-10.el9_8

almalinux advisories ALSA-2026:19145ALSA-2026:19357ALSA-2026:16799

  • krb5 Rocky Linux 10 1.21.3-10.el10_2
  • krb5 Rocky Linux 9 1.21.1-10.el9_8
  • krb5 Rocky Linux 8 1.18.2-34.el8_10

rocky linux advisories RLSA-2026:19145RLSA-2026:19357RLSA-2026:16799

  • krb5 Azure Linux 3.0 1.21.3-4

azure linux advisories AZL-85238

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

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-2026-40356 updated cvss 5.9

krb5: MIT Kerberos 5 (krb5): Denial of Service via integer underflow and out-of-bounds read

  • Red Hat Enterprise Linux 6 krb5, libkadm5, krb5-libs, krb5-server, krb5-server-ldap, krb5-workstation, +1 more Red Hat Enterprise Linux 7 krb5, libkadm5, krb5-libs, krb5-pkinit, krb5-server, krb5-server-ldap, +1 more Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.17 cert-manager/cert-manager-operator-rhel9 1791788287, cert-manager/jetstack-cert-manager-rhel9 1791371069, cert-manager/cert-manager-operator-bundle 1791970484, cert-manager/jetstack-cert-manager-acmesolver-rhel9 1791371080
    fixed: vendor fix RHSA-2026:82888
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.18 cert-manager/cert-manager-operator-rhel9 1789029076, cert-manager/jetstack-cert-manager-rhel9 1791459711, cert-manager/cert-manager-istio-csr-rhel9 1791459759, cert-manager/cert-manager-operator-bundle 1791966259, cert-manager/jetstack-cert-manager-acmesolver-rhel9 1791459707
    fixed: vendor fix RHSA-2026:82354
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.20 cert-manager/cert-manager-trust-manager-rhel9 1790598593
    fixed: vendor fix RHSA-2026:72502
  • Red Hat OpenShift API for Data Protection 1.6 oadp/oadp-velero-rhel9 1784058822
    fixed: vendor fix RHSA-2026:43692
  • Red Hat Discovery 2 discovery/discovery-ui-rhel9 1782166952, discovery/discovery-server-rhel9 1782159791
    fixed: vendor fix RHSA-2026:29197
  • Red Hat Enterprise Linux AppStream (v. 9) krb5-devel 1.21.1-10.el9_8, krb5-debuginfo 1.21.1-10.el9_8, krb5-debugsource 1.21.1-10.el9_8, libkadm5-debuginfo 1.21.1-10.el9_8, krb5-libs-debuginfo 1.21.1-10.el9_8, krb5-pkinit-debuginfo 1.21.1-10.el9_8, +4 more
    fixed: vendor fix RHSA-2026:19357
  • Red Hat Enterprise Linux AppStream (v. 10) krb5-devel 1.21.3-10.el10_2, krb5-debuginfo 1.21.3-10.el10_2, krb5-debugsource 1.21.3-10.el10_2, libkadm5-debuginfo 1.21.3-10.el10_2, krb5-libs-debuginfo 1.21.3-10.el10_2, krb5-pkinit-debuginfo 1.21.3-10.el10_2, +4 more
    fixed: vendor fix RHSA-2026:19145
show 14 more
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) krb5-devel 1.20.1-9.el9_2.6
    fixed: vendor fix RHSA-2026:24685
  • Red Hat Enterprise Linux AppStream E4S (v.9.4) krb5-devel 1.21.1-2.el9_4.5, krb5-debuginfo 1.21.1-2.el9_4.5, krb5-debugsource 1.21.1-2.el9_4.5, libkadm5-debuginfo 1.21.1-2.el9_4.5, krb5-libs-debuginfo 1.21.1-2.el9_4.5, krb5-pkinit-debuginfo 1.21.1-2.el9_4.5, +3 more
    fixed: vendor fix RHSA-2026:24686
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) krb5-devel 1.21.1-8.el9_6.2, krb5-debuginfo 1.21.1-8.el9_6.2, krb5-debugsource 1.21.1-8.el9_6.2, libkadm5-debuginfo 1.21.1-8.el9_6.2, krb5-libs-debuginfo 1.21.1-8.el9_6.2, krb5-pkinit-debuginfo 1.21.1-8.el9_6.2, +3 more
    fixed: vendor fix RHSA-2026:24683
  • Red Hat Enterprise Linux BaseOS (v. 8) krb5 1.18.2-34.el8_10, libkadm5 1.18.2-34.el8_10, krb5-libs 1.18.2-34.el8_10, krb5-pkinit 1.18.2-34.el8_10, krb5-server 1.18.2-34.el8_10, krb5-server-ldap 1.18.2-34.el8_10, +1 more
    fixed: vendor fix RHSA-2026:16799
  • Red Hat Enterprise Linux BaseOS (v. 9) krb5 1.21.1-10.el9_8, libkadm5 1.21.1-10.el9_8, krb5-libs 1.21.1-10.el9_8, krb5-pkinit 1.21.1-10.el9_8, krb5-server 1.21.1-10.el9_8, krb5-server-ldap 1.21.1-10.el9_8, +2 more
    fixed: vendor fix RHSA-2026:19357
  • Red Hat Enterprise Linux BaseOS (v. 10) krb5 1.21.3-10.el10_2, libkadm5 1.21.3-10.el10_2, krb5-libs 1.21.3-10.el10_2, krb5-pkinit 1.21.3-10.el10_2, krb5-server 1.21.3-10.el10_2, krb5-server-ldap 1.21.3-10.el10_2, +2 more
    fixed: vendor fix RHSA-2026:19145
  • Red Hat Enterprise Linux BaseOS E4S (v.9.2) krb5 1.20.1-9.el9_2.6, libkadm5 1.20.1-9.el9_2.6, krb5-libs 1.20.1-9.el9_2.6, krb5-pkinit 1.20.1-9.el9_2.6, krb5-server 1.20.1-9.el9_2.6, krb5-server-ldap 1.20.1-9.el9_2.6, +1 more
    fixed: vendor fix RHSA-2026:24685
  • Red Hat Enterprise Linux BaseOS E4S (v.9.4) krb5 1.21.1-2.el9_4.5, libkadm5 1.21.1-2.el9_4.5, krb5-libs 1.21.1-2.el9_4.5, krb5-pkinit 1.21.1-2.el9_4.5, krb5-server 1.21.1-2.el9_4.5, krb5-server-ldap 1.21.1-2.el9_4.5, +1 more
    fixed: vendor fix RHSA-2026:24686
  • Red Hat Enterprise Linux BaseOS EUS (v.9.6) krb5 1.21.1-8.el9_6.2, libkadm5 1.21.1-8.el9_6.2, krb5-libs 1.21.1-8.el9_6.2, krb5-pkinit 1.21.1-8.el9_6.2, krb5-server 1.21.1-8.el9_6.2, krb5-server-ldap 1.21.1-8.el9_6.2, +1 more
    fixed: vendor fix RHSA-2026:24683
  • Red Hat Hardened Images krb5 1.22.2-7.hum1, krb5-libs 1.22.2-7.hum1, krb5-tests 1.22.2-7.hum1, krb5-pkinit 1.22.2-7.hum1, krb5-server 1.22.2-7.hum1, krb5-server-ldap 1.22.2-7.hum1, +2 more
    fixed: vendor fix RHSA-2026:12220
  • Red Hat Insights proxy 1.5 insights-proxy/insights-proxy-container-rhel9 1780420428
    fixed: vendor fix RHSA-2026:22634
  • Red Hat OpenShift AI 3.4 rhai/base-image-neuron-rhel9 1790703542
    fixed: vendor fix RHSA-2026:74674
  • Red Hat Update Infrastructure 5 rhui5/cds-rhel9 1779798159, rhui5/rhua-rhel9 1779798222, rhui5/haproxy-rhel9 1779798164, rhui5/rhua-tp-rhel9 1787241260, rhui5/installer-rhel9 1779798165, rhui5/installer-tp-rhel9 1787135742, +1 more
    fixed: vendor fix RHSA-2026:58981
  • Red Hat OpenShift API for Data Protection 1.6 oadp/oadp-rhel9-operator 1784059086, oadp/oadp-non-admin-rhel9 1784059055, oadp/oadp-operator-bundle 1784060839, oadp/oadp-mustgather-rhel9 1784058949, oadp/oadp-vmfr-access-rhel9 1784059129, oadp/oadp-cli-binaries-rhel9 1784059134, +13 more Red Hat Hardened Images libkadm5 1.22.2-7.hum1 Red Hat Update Infrastructure 5 rhui5/cds-tp-rhel9 1787241206
    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
no
Technical impact
partial
Assessed
6 mo ago

Exploit prediction

0.60% chance of exploitation in the next 30 days, higher than 49% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • cems.fun https://cems.fun/2026/04/27/krb5-two-unauthenticated-network-vulnerabilities.html referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

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

Affected packages

ecosystem package affected fixed in
julia Kerberos_krb5_jll
all versions
 no fix listed

Affected products

  • MIT Kerberos 5

Classification

Weakness
  • CWE-191 Integer Underflow (Wrap or Wraparound)

References

Sources

Fencer Vulns 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.