PT-2020-6126 · Lxml+9 · Lxml+9

Published 2020-07-19 · Updated 2025-01-14 · CVE-2021-28957

Positive Technologies (AI Summary)

CVSS v3.1

9.1

Critical

Base vector

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Name of the Vulnerable Software and Affected Versions lxml versions prior to 4.6.3

Description A remote attacker could exploit this flaw to run arbitrary JS code on users who interact with incorrectly sanitized HTML. The issue arises when the safe attrs only and forms arguments are disabled in the Cleaner class, allowing the formaction attribute to bypass the sanitizer.

Recommendations For versions prior to 4.6.3, update to version 4.6.3 to resolve the issue. As a temporary workaround, consider enabling the safe attrs only and forms arguments in the Cleaner class to prevent the formaction attribute from bypassing the sanitizer. Restrict access to the Cleaner class until the issue is resolved.

Exploit

Fix

XSS

Weakness Enumeration

CWE-79

Related Identifiers

ALSA-2021:4151

ALSA-2021:4158

ALSA-2021:4160

ALSA-2021:4162

ALT-PU-2021-1529

AZL-6808

BDU:2021-03119

CESA-2021_4151

CESA-2021_4158

CESA-2021_4160

CESA-2021_4162

CVE-2021-28957

DLA-2606-1

DSA-4880-1

GHSA-JQ4V-F5Q6-MJQQ

MGASA-2021-0246

OESA-2021-1178

OPENSUSE-SU-2022:0803-1

OPENSUSE-SU-2022_0803-1

OPENSUSE-SU-2022_3836-1

OPENSUSE-SU-2024:11236-1

OPENSUSE-SU-2024:11473-1

OPENSUSE-SU-2025:14647-1

PYSEC-2021-19

RHSA-2021:3254

RHSA-2021:4151

RHSA-2021:4158

RHSA-2021:4160

RHSA-2021:4162

RHSA-2021_4151

RHSA-2021_4158

RHSA-2021_4160

RHSA-2021_4162

RLSA-2021:4151

RLSA-2021:4158

RLSA-2021:4160

RLSA-2021:4162

SUSE-FU-2022:0444-1

SUSE-FU-2022:0445-1

SUSE-SU-2022:0803-1

SUSE-SU-2022:0895-1

SUSE-SU-2022:1536-1

SUSE-SU-2022:1729-1

SUSE-SU-2022:3836-1

SUSE-SU-2022:3934-1

SUSE-SU-2022:3937-1

SUSE-SU-2022_3934-1

SUSE-SU-2022_3937-1

USN-4896-1

USN-4896-2

Affected Products

Alt Linux

Almalinux

Astra Linux

Centos

Linuxmint

Red Hat

Rocky Linux

Suse

Ubuntu

Lxml

References · 159

• 🔥 https://bugs.launchpad.net/lxml/+bug/1888153 · Exploit
• https://github.com/lxml/lxml/pull/316/commits/10ec1b4e9f93713513a3264ed6158af22492f270 · Patch
• https://github.com/lxml/lxml/commit/a5f9cb52079dc57477c460dbe6ba0f775e14a999 · Patch
• https://osv.dev/vulnerability/USN-4896-2 · Vendor Advisory
• https://security.gentoo.org/glsa/202208-06 · Vendor Advisory
• https://osv.dev/vulnerability/ALSA-2021:4160 · Vendor Advisory
• https://osv.dev/vulnerability/SUSE-SU-2022:3934-1 · Vendor Advisory
• https://osv.dev/vulnerability/RLSA-2021:4162 · Vendor Advisory
• https://linux.oracle.com/errata/ELSA-2021-4160.html · Vendor Advisory
• https://osv.dev/vulnerability/AZL-6808 · Vendor Advisory
• https://ubuntu.com/security/CVE-2021-28957 · Vendor Advisory
• https://osv.dev/vulnerability/PYSEC-2021-19 · Vendor Advisory
• https://linux.oracle.com/errata/ELSA-2021-4151.html · Vendor Advisory
• https://errata.almalinux.org/8/ALSA-2021-4162.html · Vendor Advisory
• https://osv.dev/vulnerability/openSUSE-SU-2025:14647-1 · Vendor Advisory