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Fencer Intel
medium 6.5

CVE-2021-4209 json

A NULL pointer dereference flaw was found in GnuTLS.

published 4y ago modified 26d ago also EUVD-2021-34067 , JLSEC-2026-522

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.9%
EPSS 1.9% chance of exploitation in 30 days, percentile 79%
public exploits
0
none known

Summary

A NULL pointer dereference flaw was found in GnuTLS. As Nettle's hash update functions internally call memcpy, providing zero-length input may cause undefined behavior. This flaw leads to a denial of service after authentication in rare circumstances.

Patch / fix

  • julia GnuTLS_jll 3.7.8+0
  • 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
  • gnutls28 Debian 14, Debian 13, Debian 12 3.7.3-2

debian advisories DEBIAN-CVE-2021-4209

  • gnutls28 Ubuntu 18.04 LTS 3.5.18-1ubuntu1.6
  • gnutls28 Ubuntu 20.04 LTS 3.6.13-2ubuntu1.7
  • gnutls28 Ubuntu Pro 16.04 LTS 3.4.10-4ubuntu1.9+esm1

ubuntu advisories UBUNTU-CVE-2021-4209

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

  • gnutls SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +7 more 3.6.7-150000.6.45.2
  • gnutls SLE Real Time 15 SP2, SLE Module for Basesystem 15 SP3, SLE Micro 5.1 +1 more 3.6.7-14.16.1
  • gnutls SLES for SAP 12 SP5, SLES 12 SP5 3.4.17-8.11.1
  • gnutls SLES for SAP 12 SP5, SLES 12 SP5, SLE Software Development Kit 12 SP5 3.3.27-3.6.1

suse advisories SUSE-SU-2022:2830-1SUSE-SU-2022:0717-1SUSE-SU-2022:0678-1SUSE-SU-2022:0677-1

  • gnutls openSUSE Leap 15.3 3.6.7-14.16.1

opensuse advisories openSUSE-SU-2022:0717-1

Is CVE-2021-4209 in your dependencies? 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-2021-4209 updated cvss 6.5

GnuTLS: Null pointer dereference in MD_UPDATE

  • Red Hat Enterprise Linux 6 gnutls, gnutls-guile, gnutls-utils Red Hat Enterprise Linux 7 gnutls, gnutls-c++, gnutls-dane, gnutls-utils
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 gnutls, gnutls-c++, gnutls-dane, gnutls-utils
    affected: workaround, no fix planned “Will not fix”
  • Red Hat Enterprise Linux 9 gnutls, gnutls-c++, gnutls-dane, gnutls-utils
    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

1.91% chance of exploitation in the next 30 days, higher than 79% 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
OSV 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
julia GnuTLS_jll
<3.7.8+0
3.7.8+0

Affected products

  • n/a GnuTLS
  • 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.