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Fencer Intel
medium 6.5

CVE-2021-37750 json

The Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.18.5 and 1.19.x before 1.19.3 has a NULL pointer dereference in kdc…

published 5y ago modified 26d ago also EUVD-2021-24231

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
2.5%
EPSS 2.5% chance of exploitation in 30 days, percentile 84%
public exploits
0
none known

Summary

The Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.18.5 and 1.19.x before 1.19.3 has a NULL pointer dereference in kdc/do_tgs_req.c via a FAST inner body that lacks a server field.

Patch / fix

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • krb5 Debian 14, Debian 13, Debian 12 1.18.3-7

debian advisories DEBIAN-CVE-2021-37750

  • krb5 Ubuntu 18.04 LTS 1.16-2ubuntu0.4
  • krb5 Ubuntu 20.04 LTS 1.17-6ubuntu4.3

ubuntu advisories UBUNTU-CVE-2021-37750

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 7 1.15.1-51.el7_9
  • libkadm5 RHEL 7 1.15.1-51.el7_9
  • krb5-libs RHEL 7 1.15.1-51.el7_9
  • krb5-pkinit RHEL 7 1.15.1-51.el7_9
  • krb5-server RHEL 7 1.15.1-51.el7_9
  • krb5-server-ldap RHEL 7 1.15.1-51.el7_9
  • krb5-workstation RHEL 7 1.15.1-51.el7_9
  • krb5 RHEL 8 1.18.2-8.3.el8_4

red hat advisories RHSA-2021:4788RHSA-2021:3576

  • krb5 SLES for SAP 12 SP5, SLES 12 SP5, SLE Software Development Kit 12 SP5 1.16.3-46.12.1
  • krb5 SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 1.15.2-150000.6.17.1
  • krb5 SLE Module for Server Applications 15 SP3, SLE Module for Server Applications 15 SP2, SLE Module for Basesystem 15 SP3 +3 more 1.16.3-3.24.1

suse advisories SUSE-SU-2024:1702-1SUSE-SU-2022:4154-1SUSE-SU-2021:3454-2SUSE-SU-2021:3454-1

  • krb5 openSUSE Tumbleweed 1.19.2-2.2
  • krb5 openSUSE Leap 15.2 1.16.3-lp152.5.22.1
  • krb5-mini openSUSE Leap 15.2 1.16.3-lp152.5.22.1
  • krb5 openSUSE Leap 15.3 1.16.3-3.24.1

opensuse advisories openSUSE-SU-2024:10899-1openSUSE-SU-2021:1411-1openSUSE-SU-2021:3454-1

  • krb5 Rocky Linux 8 1.18.2-8.3.el8_4

rocky linux advisories RLSA-2021:3576

  • krb5 Alpine 3.14, Alpine 3.13, Alpine 3.12 1.18.5-r0
  • krb5 Alpine 3.24, Alpine 3.23, Alpine 3.22 +7 more 1.19.3-r0

alpine advisories ALPINE-CVE-2021-37750

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

  • krb5 CBL-Mariner 2.0 1.19.3-1

azure linux advisories AZL-6608

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

  • krb5 Arch Linux 1.19.3-1

arch linux advisories AVG-2312

Is CVE-2021-37750 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-2021-37750 updated cvss 6.5

krb5: NULL pointer dereference in process_tgs_req() in kdc/do_tgs_req.c via a FAST inner body that lacks server field

  • Red Hat Enterprise Linux BaseOS (v. 8) krb5 1.18.2-8.3.el8_4, libkadm5 1.18.2-8.3.el8_4, krb5-libs 1.18.2-8.3.el8_4, krb5-pkinit 1.18.2-8.3.el8_4, krb5-server 1.18.2-8.3.el8_4, krb5-server-ldap 1.18.2-8.3.el8_4, +1 more
    fixed: vendor fix RHSA-2021:3576
  • Red Hat Enterprise Linux Client (v. 7) krb5 1.15.1-51.el7_9, libkadm5 1.15.1-51.el7_9, krb5-libs 1.15.1-51.el7_9, krb5-pkinit 1.15.1-51.el7_9, krb5-workstation 1.15.1-51.el7_9 Red Hat Enterprise Linux Client Optional (v. 7) krb5-server 1.15.1-51.el7_9, krb5-server-ldap 1.15.1-51.el7_9 Red Hat Enterprise Linux ComputeNode Optional (v. 7) krb5-server 1.15.1-51.el7_9, krb5-server-ldap 1.15.1-51.el7_9 Red Hat Enterprise Linux Server (v. 7) krb5 1.15.1-51.el7_9, libkadm5 1.15.1-51.el7_9, krb5-libs 1.15.1-51.el7_9, krb5-pkinit 1.15.1-51.el7_9, krb5-server 1.15.1-51.el7_9, krb5-server-ldap 1.15.1-51.el7_9, +1 more Red Hat Enterprise Linux Workstation (v. 7) krb5 1.15.1-51.el7_9, libkadm5 1.15.1-51.el7_9, krb5-libs 1.15.1-51.el7_9, krb5-pkinit 1.15.1-51.el7_9, krb5-server 1.15.1-51.el7_9, krb5-server-ldap 1.15.1-51.el7_9, +1 more
    fixed: vendor fix RHSA-2021:4788
  • Red Hat Enterprise Linux 6 krb5, libkadm5, krb5-libs, krb5-server, krb5-server-ldap, krb5-workstation, +1 more Red Hat Enterprise Linux 9 krb5, libkadm5, krb5-libs, krb5-pkinit, krb5-server, krb5-server-ldap, +2 more Red Hat JBoss Core Services krb5 Red Hat JBoss Enterprise Application Platform 6 krb5
    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 ICSA-23-348-10 updated cvss 6.5

Siemens SIMATIC S7-1500

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.0, < 3.1.5
    affected: fixed in V3.1.5, mitigation support.industry.siemens.com

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

2.51% chance of exploitation in the next 30 days, higher than 84% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 4.0 AV:N/AC:L/Au:S/C:N/I:N/A:P

Affected products

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

Classification

Weakness

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.