CVE-2021-28957

MEDIUM
6.1
CVSS Score
Published: March 21, 2021 at 04:39 AM UTC
Updated: June 17, 2026 at 03:47 AM UTC
5 products affected across 5 vendorsDebian LinuxFedoraSnapCenter

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Severity
MEDIUM6.1
Exploit prediction
EPSS 4%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 4.6.3
Affected range stops below 4.6.3, so it looks safe — our inference, not a vendor statement
All versions

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

6.1MEDIUMCISA-ADP
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-79

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