GitStock

mozilla/bleach · Security

Bleach vulnerable to mutation XSS via whitelisted math or svg and raw tag

GHSA ID
GHSA-m6xf-fq7q-8743
CVE ID
CVE-2020-6816
Severity
medium
Published
Updated
CVSS
6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CVSS v3
6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CVSS v4
5.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

Description

Impact

A mutation XSS affects users calling bleach.clean with all of:

  • the svg or math in the allowed/whitelisted tags
  • an RCDATA tag (see below) in the allowed/whitelisted tags
  • the keyword argument strip=False

Patches

Users are encouraged to upgrade to bleach v3.1.2 or greater.

Workarounds

  • modify bleach.clean calls to use strip=True, or not whitelist math or svg tags and one or more of the following tags:
script
noscript
style
noframes
xmp
noembed
iframe

References

Credits

  • Reported by Yaniv Nizry from the CxSCA AppSec group at Checkmarx

For more information

If you have any questions or comments about this advisory:

CWEs

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

References