CVE-2021-28957

Aliases:GHSA-jq4v-f5q6-mjqqPYSEC-2021-19
Advisory lineage Upstream: 0 Downstream: 22
Modified
Published: 21 Mar 2021, 04:39
Last modified:17 Dec 2025, 21:31

Vulnerability Summary

Overall Risk (default)
medium
35/100
CVSS Score
6.1 MEDIUM
v3.1 (cve.org)
EPSS Score
0.52% LOW
1% probability +0.02%
KEV
Not listed
Ransomware
No reports
Public exploits
1 found
Dark Web
Not detected

Timeline

21 Mar 2021, 04:39
Published
Vulnerability first disclosed
17 Dec 2025, 21:31
Last Modified
Vulnerability information updated

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 Metrics

  • v4.0•MEDIUM•Score: 5.3CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
  • v3.1•MEDIUM•Score: 6.1CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
  • v2.0•MEDIUM•Score: 4.3AV:N/AC:M/Au:N/C:N/I:P/A:N

EPSS Trends

Current EPSS score: 0.52%• Percentile: 67%

Techniques & Countermeasures

  • CWE-79•Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

    The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

Affected Systems

  • debian•debian_linux

    9.0 | 10.0

  • fedoraproject•fedora

    33 | 34

  • lxml•lxml

    < 4.6.3

  • netapp•snapcenter

    na

  • oracle•zfs_storage_appliance_kit

    8.8

  • PyPI•lxml

    < a5f9cb52079dc57477c460dbe6ba0f775e14a999 | < 4.6.3

References (20)