CVE-2021-28957

mediumpriority · track · 25EPSS 0.040 · 91 %ileDEEURUUS

grimoire priorityP3 · Track

Exploitable?

—

no known exploitation

Likely / severe?

4.04% (91st) EPSS

CVSS 4.3 · medium

Is it mine?

49 products

Check your exposure

Who says so?

6 sources

cnnvd · enisa_euvd · fstec_bdu · osv

EPSS · scored 2026-10-26

An XSS vulnerability was discovered in python-lxml's clean module versions before 4.6.3. When disabling the safe_attrs_only and forms arguments, the Cleaner class does not remove the formaction attribute allowing for JS to bypass the sanitizer. A remote attacker could exploit this flaw to run arbitrary JS code on users who interact with incorrectly sanitized HTML. This issue is patched in lxml 4.6.3.

remediations

Vendor fix, mitigation, or workaround guidance, as published by each source.

A vendor fix is available.

Fixedpython-lxml-0:4.2.3-3.el8.src as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158
Fixedpython-lxml-debugsource-0:4.2.3-3.el8.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158
Fixedpython-lxml-debugsource-0:4.2.3-3.el8.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158
Fixedpython-lxml-debugsource-0:4.2.3-3.el8.s390x as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158
Fixedpython-lxml-debugsource-0:4.2.3-3.el8.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158
Fixedpython3-lxml-0:4.2.3-3.el8.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158
Fixedpython3-lxml-0:4.2.3-3.el8.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158
Fixedpython3-lxml-0:4.2.3-3.el8.s390x as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158
Fixedpython3-lxml-0:4.2.3-3.el8.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158
Fixedpython3-lxml-debuginfo-0:4.2.3-3.el8.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158
Fixedpython3-lxml-debuginfo-0:4.2.3-3.el8.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158
Fixedpython3-lxml-debuginfo-0:4.2.3-3.el8.s390x as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158
Fixedpython3-lxml-debuginfo-0:4.2.3-3.el8.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 8)redhat_csaf
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
https://access.redhat.com/errata/RHSA-2021:4158

cvss

Technical severity, 0–10. One row per scoring source.

6.1

010

base score 0–10 · higher = more severe · hover a vector to decode

v2.04.3mediumAV:N/AC:M/Au:N/C:N/I:P/A:Nprimary · NVD / NIST USexploitability 8.6 · impact 2.9

v3.16.1mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:Nprimary · NVD / NIST USexploitability 2.8 · impact 2.7

v3.16.1mediumAV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:Nsecondary · FSTEC (BDU) RU

v3.16.1mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:Nsecondary · ENISA EU

v3.16.1mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:Nsecondaryexploitability 2.8 · impact 2.7

v3.16.1mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:Nsecondary · OSV

v3.15.6mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N/E:Usecondary · CVSS-BT (t0sche)

v3.16.1mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:Nsecondary · Red Hat Product Security US

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Trackcoordinatorcisa_ssvcUS

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-79USprimaryCWE-79USCWE-79USCWE-79US

affected products (49)

Products and version ranges known to be affected.

Amazon Linux 2all versionscert_bundDEcpe:/o:amazon:linux_2:-
Avaya Aura Experience Portalall versionscert_bundDEcpe:/a:avaya:aura_experience_portal:-
Debian Linuxall versionscert_bundDEcpe:/o:debian:debian_linux:-
Gentoo Linuxall versionscert_bundDEcpe:/o:gentoo:linux:-
IBM Security Verify Access 10.0.0-10.0.7.1all versionscert_bundDEcpe:/a:ibm:security_verify_access:10.0.0_-_10.0.7.1
Oracle Linuxall versionscert_bundDEcpe:/o:oracle:linux:-
RESF Rocky Linuxall versionscert_bundDEcpe:/o:resf:rocky_linux:-
Red Hat Enterprise Linuxall versionscert_bundDEcpe:/o:redhat:enterprise_linux:-
Red Hat Enterprise Linux 8all versionscert_bundDEcpe:/o:redhat:enterprise_linux:8
Red Hat OpenShift Data Foundation <4.12.10all versionscert_bundDE
SUSE Linuxall versionscert_bundDEcpe:/o:suse:suse_linux:-
SUSE openSUSEall versionscert_bundDEcpe:/o:suse:opensuse:-
Ubuntu Linuxall versionscert_bundDEcpe:/o:canonical:ubuntu_linux:-
Red Hat OpenShift≤ Data Foundation <4.12.10cert_bundDE
n/a n/a≤ n/aenisa_euvdEU
Fedora Project Fedora≤ 33fstec_bduRU
Fedora Project Fedora≤ 34fstec_bduRU
Stefan Behnel Lxml≤ 4.6.3fstec_bduRU
АО «Концерн ВНИИНС» ОС ОН «Стрелец»≤ 16.01.2023fstec_bduRU
АО «НППКТ» ОСОН ОСнова Оnyx≤ 2.1fstec_bduRU

showing 20 of 49

advisories (5)

Vendor and ecosystem advisories describing this.

RHSA-2021:4158Red Hat Security Advisory: python-lxml security update2021-11-09csaf · redhat_csafUS
An update for python-lxml is now available for Red Hat Enterprise Linux 8. Red Hat Product Security has rated this update as having a security impact of Moderate. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.
WID-SEC-W-2022-0571Red Hat Enterprise Linux: Mehrere SchwachstellenDeutsch2021-11-09csaf · cert_bundDE
Ein entfernter, anonymer, authentisierter oder lokaler Angreifer kann mehrere Schwachstellen in Red Hat Enterprise Linux ausnutzen, um einen Cross-Site-Scripting-Angriff durchzuführen, vertrauliche Informationen offenzulegen, einen Denial-of-Service-Zustand herbeizuführen, Sicherheitsmaßnahmen zu umgehen, beliebigen Code auszuführen, Dateien zu manipulieren und einen nicht spezifizierten Angriff durchzuführen.
WID-SEC-W-2023-0395Splunk Splunk Enterprise: Mehrere SchwachstellenDeutsch2023-02-14csaf · cert_bundDE
Ein Angreifer kann mehrere Schwachstellen in Splunk Splunk Enterprise ausnutzen, um vertrauliche Informationen offenzulegen, Sicherheitsmaßnahmen zu umgehen, einen Denial-of-Service-Zustand zu verursachen, Daten zu manipulieren und einen Cross-Site-Scripting-Angriff durchzuführen.
GHSA-jq4v-f5q6-mjqqlxml vulnerable to Cross-Site Scripting 2021-03-22ghsa · osvUS
An XSS vulnerability was discovered in the python `lxml` clean module versions before 4.6.3. When disabling `the safe_attrs_only` and `forms` arguments, the `Cleaner` class does not remove the `formaction` attribute allowing for JS to bypass the sanitizer. A remote attacker could exploit this flaw to run arbitrary JS code on users who interact with incorrectly sanitized HTML. This issue is patched in `lxml` 4.6.3.
PYSEC-2021-192021-03-21vendor · osvUS
An XSS vulnerability was discovered in python-lxml's clean module versions before 4.6.3. When disabling the safe_attrs_only and forms arguments, the Cleaner class does not remove the formaction attribute allowing for JS to bypass the sanitizer. A remote attacker could exploit this flaw to run arbitrary JS code on users who interact with incorrectly sanitized HTML. This issue is patched in lxml 4.6.3.

also known as (7)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd fstec_bdu osv cert_bund redhat_csaf NVD CVE.org MITRE

published 2021-03-21modified 2026-06-17

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+52969 more

references (49)

External citations — patches, advisories, analysis.

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