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Fencer Vulns
medium 6.5

CVE-2021-3541 json

A flaw was found in libxml2

published 2021-07-09 5 y ago modified 2026-10-14 25 d ago also EUVD-2021-26852 , JLSEC-2025-73

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
2.1%
EPSS 2.1% chance of exploitation in 30 days, percentile 81%
public exploits
0
none known

Summary

A flaw was found in libxml2. Exponential entity expansion attack its possible bypassing all existing protection mechanisms and leading to denial of service.

Patch / fix

  • julia XML2_jll 2.9.12+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
  • libxml2 Debian 14, Debian 13, Debian 12 2.9.10+dfsg-6.7

debian advisories DEBIAN-CVE-2021-3541

  • libxml2 Ubuntu 20.04 LTS 2.9.10+dfsg-5ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2021-3541

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

  • jbcs-httpd24-curl jboss core services 1 7.78.0-3.jbcs.el7
  • jbcs-httpd24-curl jboss core services 1 7.78.0-3.el8jbcs
  • jbcs-httpd24-httpd jboss core services 1 2.4.37-80.jbcs.el7
  • jbcs-httpd24-httpd jboss core services 1 2.4.37-80.el8jbcs
  • jbcs-httpd24-mod_jk jboss core services 1 1.2.48-29.redhat_1.jbcs.el7
  • jbcs-httpd24-mod_jk jboss core services 1 1.2.48-29.redhat_1.el8jbcs
  • jbcs-httpd24-mod_md jboss core services 1 1:2.0.8-41.jbcs.el7
  • jbcs-httpd24-mod_md jboss core services 1 1:2.0.8-41.el8jbcs

red hat advisories RHSA-2022:1389RHSA-2021:2569

  • libxml2 SLES for SAP 15 SP3, SLES for SAP 15 SP2, SLES for SAP 15 SP1 +14 more 2.9.7-150000.3.57.1
  • python-libxml2-python SLES for SAP 15 SP3, SLES for SAP 15 SP2, SLES for SAP 15 SP1 +14 more 2.9.7-150000.3.57.1
  • libxml2 SLES for SAP 12 SP5, SLES 12 SP5, SLE Software Development Kit 12 SP5 2.9.4-46.46.1
  • python-libxml2 SLES for SAP 12 SP5, SLES 12 SP5 2.9.4-46.46.1
  • libxml2 SLE Module for Basesystem 15 SP3, SLE Module for Basesystem 15 SP2, SLE Micro 5.0 2.9.7-3.37.1
  • python-libxml2-python SLE Module for Python 2 15 SP3, SLE Module for Python 2 15 SP2, SLE Module for Basesystem 15 SP3 +1 more 2.9.7-3.37.1

suse advisories SUSE-SU-2023:2048-1SUSE-SU-2021:2016-1SUSE-SU-2021:1917-1

  • rubygem-nokogiri openSUSE Tumbleweed 1.18.9-1.4
  • rubygem-nokogiri openSUSE Tumbleweed 1.18.2-1.1
  • rubygem-nokogiri openSUSE Tumbleweed 1.15.5-1.5
  • libxml2 openSUSE Tumbleweed 2.9.12-1.2
  • rubygem-nokogiri openSUSE Tumbleweed 1.13.3-1.1
  • ruby3.2-rubygem-nokogiri openSUSE Tumbleweed 1.13.9-1.7
  • libxml2 openSUSE Leap 15.3 2.9.7-3.37.1
  • python-libxml2-python openSUSE Leap 15.3 2.9.7-3.37.1

opensuse advisories openSUSE-SU-2026:10356-1openSUSE-SU-2025:14697-1openSUSE-SU-2024:14174-1openSUSE-SU-2024:11016-1openSUSE-SU-2024:11912-1openSUSE-SU-2024:13165-1

  • libxml2 Rocky Linux 8 2.9.7-9.el8_4.2

rocky linux advisories RLSA-2021:2569

  • libxml2 Alpine 3.12, Alpine 3.11 2.9.12-r0
  • libxml2 Alpine 3.24, Alpine 3.23, Alpine 3.22 +8 more 2.9.11-r0
  • qt5-qtwebengine Alpine 3.23, Alpine 3.22, Alpine 3.21 +7 more 5.15.3_git20211112-r0

alpine advisories ALPINE-CVE-2021-3541

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

  • libxml2 Arch Linux 2.9.11-1

arch linux advisories AVG-1883

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-2021-3541 updated cvss 6.5

libxml2: Exponential entity expansion attack bypasses all existing protection mechanisms

  • Red Hat Enterprise Linux 6 libxml2, compat-expat1, libxml2-python
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 libxml2, libxml2-python
    affected: no fix planned “Will not fix”
  • Red Hat Enterprise Linux AppStream (v. 8) libxml2-devel 2.9.7-9.el8_4.2, libxml2-debuginfo 2.9.7-9.el8_4.2, libxml2-debugsource 2.9.7-9.el8_4.2, python3-libxml2-debuginfo 2.9.7-9.el8_4.2 Red Hat Enterprise Linux BaseOS (v. 8) libxml2 2.9.7-9.el8_4.2, python3-libxml2 2.9.7-9.el8_4.2
    fixed: vendor fix RHSA-2021:2569
  • Red Hat JBoss Core Services
    fixed: vendor fix RHSA-2022:1390
  • Red Hat JBoss Core Services on RHEL 7 Server jbcs-httpd24-curl 7.78.0-3.jbcs.el7, jbcs-httpd24-httpd 2.4.37-80.jbcs.el7, jbcs-httpd24-mod_md 2.0.8-41.jbcs.el7, jbcs-httpd24-libcurl 7.78.0-3.jbcs.el7, jbcs-httpd24-apr-util 1.6.1-91.jbcs.el7, jbcs-httpd24-mod_ssl 2.4.37-80.jbcs.el7, +25 more Red Hat JBoss Core Services on RHEL 8 jbcs-httpd24-curl 7.78.0-3.el8jbcs, jbcs-httpd24-httpd 2.4.37-80.el8jbcs, jbcs-httpd24-mod_md 2.0.8-41.el8jbcs, jbcs-httpd24-libcurl 7.78.0-3.el8jbcs, jbcs-httpd24-apr-util 1.6.1-91.el8jbcs, jbcs-httpd24-mod_ssl 2.4.37-80.el8jbcs, +25 more
    fixed: vendor fix RHSA-2022:1389
  • Red Hat Migration Toolkit 1.4 rhmtc/openshift-migration-ui-rhel8 v1.4.6-4, rhmtc/openshift-velero-plugin-rhel8 v1.4.6-4, rhmtc/openshift-migration-velero-rhel8 v1.4.6-5, rhmtc/openshift-migration-registry-rhel8 v1.4.6-4, rhmtc/openshift-migration-operator-bundle v1.4.6-5, rhmtc/openshift-migration-controller-rhel8 v1.4.6-4, +7 more
    fixed: vendor fix RHBA-2021:2854
  • Red Hat Enterprise Linux 9 libxml2, python3-libxml2
    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

cisa ICSA-21-336-06 updated cvss 6.5

Hitachi Energy APM Edge

  • Hitachi Energy APM Edge 3.0, 2.0, 1.0
    affected: vendor fix, mitigation “Physically protect process control systems from direct access by unauthorized personnel.” search.abb.com

From CISA ICS and IT advisories (CSAF, https://github.com/cisagov/CSAF), a U.S. Government work; changed: reduced to products, statuses and remediations. CISA notification · csaf

Exploit prediction

2.07% chance of exploitation in the next 30 days, higher than 81% of all scored CVEs (FIRST EPSS, 2026-11-08).

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
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 XML2_jll
<2.9.12+0
2.9.12+0

Affected products

  • n/a libxml2
  • 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
  • CWE-776 Improper Restriction of Recursive Entity References in DTDs

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.