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CVE-2021-28957

Published: 21 March 2021

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.

Priority

Medium

Cvss 3 Severity Score

6.1

Score breakdown

Status

Package Release Status
lxml
Launchpad, Ubuntu, Debian
bionic
Released (4.2.1-1ubuntu0.4)
focal
Released (4.5.0-1ubuntu0.3)
groovy
Released (4.5.2-1ubuntu0.4)
trusty
Released (3.3.3-1ubuntu0.2+esm3)
Available with Ubuntu Pro or Ubuntu Pro (Infra-only)
upstream
Released (4.6.3-1)
xenial
Released (3.5.0-1ubuntu0.4)
Patches:
upstream: https://github.com/lxml/lxml/commit/2d01a1ba8984e0483ce6619b972832377f208a0d

Severity score breakdown

Parameter Value
Base score 6.1
Attack vector Network
Attack complexity Low
Privileges required None
User interaction Required
Scope Changed
Confidentiality Low
Integrity impact Low
Availability impact None
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N