Headline
CVE-2020-6802: mutation XSS in bleach.clean when noscript and raw tag whitelisted
In Mozilla Bleach before 3.11, a mutation XSS affects users calling bleach.clean with noscript and a raw tag in the allowed/whitelisted tags option.
Impact
A mutation XSS affects users calling bleach.clean with noscript and a raw tag (see below) in the allowed/whitelisted tags option.
Patches
v3.1.1
Workarounds
modify bleach.clean calls to not whitelist noscript and one or more of the following raw tags:
title textarea script style noembed noframes iframe xmp
- A strong Content-Security-Policy without unsafe-inline and unsafe-eval script-srcs) will also help mitigate the risk.
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=1615315
- https://cure53.de/fp170.pdf
- https://nvd.nist.gov/vuln/detail/CVE-2020-6802
- https://www.checkmarx.com/blog/vulnerabilities-discovered-in-mozilla-bleach
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:
- Open an issue at https://github.com/mozilla/bleach/issues
- Email us at security@mozilla.org