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Fencer Vulns
high 7.8

CVE-2021-3516 json

There's a flaw in libxml2's xmllint in versions before 2.9.11.

published 2021-06-01 5 y ago modified 2026-10-14 26 d ago also EUVD-2021-26834

cvss
7.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
2.0%
EPSS 2.0% chance of exploitation in 30 days, percentile 81%
public exploits
0
none known

Summary

There's a flaw in libxml2's xmllint in versions before 2.9.11. An attacker who is able to submit a crafted file to be processed by xmllint could trigger a use-after-free. The greatest impact of this flaw is to confidentiality, integrity, and availability.

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
  • libxml2 Debian 14, Debian 13, Debian 12 2.9.10+dfsg-6.6

debian advisories DEBIAN-CVE-2021-3516

  • libxml2 Ubuntu 18.04 LTS 2.9.4+dfsg1-6.1ubuntu1.4
  • libxml2 Ubuntu 20.04 LTS 2.9.10+dfsg-5ubuntu0.20.04.1
  • libxml2 Ubuntu Pro 14.04 LTS 2.9.1+dfsg1-3ubuntu4.13+esm2
  • libxml2 Ubuntu Pro 16.04 LTS 2.9.3+dfsg1-1ubuntu0.7+esm1

ubuntu advisories UBUNTU-CVE-2021-3516

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 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +11 more 2.9.4-46.43.1
  • python-libxml2 SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +10 more 2.9.4-46.43.1
  • libxml2 SLE Module for Basesystem 15 SP3, SLE Module for Basesystem 15 SP2, SLE Micro 5.0 2.9.7-3.34.1
  • 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 2.9.7-3.34.1
  • libxml2 SLES 11 SP4-LTSS, SLE Point of Sale 11 SP3 2.7.6-0.77.36.1
  • libxml2-python SLES 11 SP4-LTSS, SLE Point of Sale 11 SP3 2.7.6-0.77.36.1
  • libxml2 SLES for SAP 12 SP5, SLES 12 SP5, SLE Software Development Kit 12 SP5 2.9.4-46.40.1
  • python-libxml2 SLES for SAP 12 SP5, SLES 12 SP5 2.9.4-46.40.1

suse advisories SUSE-SU-2021:1658-1SUSE-SU-2021:1654-1SUSE-SU-2021:14729-1SUSE-SU-2021:1524-1SUSE-SU-2021:1523-1

  • 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 15.2 2.9.7-lp152.10.12.1
  • python-libxml2-python openSUSE Leap 15.2 2.9.7-lp152.10.12.1

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 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-2021-3516 updated cvss 7.8

libxml2: Use-after-free in xmlEncodeEntitiesInternal() in entities.c

  • Red Hat Enterprise Linux 6 libxml2, compat-expat1, libxml2-python Red Hat Enterprise Linux 7 libxml2, libxml2-python
    affected: workaround, no fix planned “This flaw can be mitigated by not using xmllint with the --html and --push options together.”
  • 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 “This flaw can be mitigated by not using xmllint with the --html and --push options together.” RHSA-2021:2569
  • Red Hat JBoss Core Services
    fixed: vendor fix “This flaw can be mitigated by not using xmllint with the --html and --push options together.” 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 “This flaw can be mitigated by not using xmllint with the --html and --push options together.” 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 “This flaw can be mitigated by not using xmllint with the --html and --push options together.” 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 7.8

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 7.8

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

2.04% chance of exploitation in the next 30 days, higher than 81% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • gitlab.gnome.org https://gitlab.gnome.org/GNOME/libxml2/-/issues/230 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
NVD 2.0 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P

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

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.