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CVE-2021-28957

Published: Mar 21, 2021Updated: Dec 17, 2025 Sources: CVE List NVD GHSA BDUCWE-79
NVD MITRE
6.1CVSSMEDIUM
EPSS Score
4.0%
Top 10.8%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

Description

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.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:RS:CC:LI:LA:N
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:RUser Interaction
Required
Scope
S:CScope
Changed
Impact
C:LConfidentiality
Low
I:LIntegrity
Low
A:NAvailability
None
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Weaknesses

CWE-79

Affected Products

lxmllxml
Library
OSS Libraries / generic-library
debian linuxdebian
On-premOS
Operating Systems / linux-distro
fedorafedoraproject
On-premOS
Operating Systems / linux-distro
snapcenternetappHardware Firmware
zfs storage appliance kitoracle
On-premDatabase
Databases / data-warehouse-analytics
lxmloss-projectOSS Librariesaka lxml/lxml
debianoss-projectGBOperating Systemsaka debian gnu/linux
fedoraprojectoss-projectUSOperating Systemsaka fedora project
netappcommercialUSHardware Firmware
oraclecommercialUSDatabasesaka oracle corp.
and 11 more affected products View all →

Attack Graph

Products CVE Techniques Tactics

Click technique nodes to view MITRE ATT&CK details. Scroll to zoom, drag to pan.

Exploitability

Official Patch Available

MITRE ATT&CK

2 techniques
Execution
Initial Access
View detailed technique mapping

References

https://bugs.launchpad.net/lxml/+bug/1888153
bugs.launchpad.net
https://github.com/lxml/lxml/commit/a5f9cb52079dc57477c460dbe6ba0f775e14a999
github.com
https://github.com/lxml/lxml/pull/316/commits/10ec1b4e9f93713513a3264ed6158af22492f270
github.com
and 32 more references View all →

Timeline

Published
Mar 21, 2021
Last Updated
Dec 17, 2025

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