XSS in Bleach when noscript and raw tag whitelistedGHSA-q65m-pv3f-wr5r
MEDIUMFix: mozilla/bleach@f77e0f6GHSA-q65m-pv3f-wr5r is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in bleach. 2 public exploit references exist, so weaponization risk is real. A fix is available for bleach — see the affected versions and patch details below.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
GHSA-q65m-pv3f-wr5r by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 397,508 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
bleachReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
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.cleancalls to not whitelistnoscriptand one or more of the following raw tags:
title
textarea
script
style
noembed
noframes
iframe
xmp
- A strong Content-Security-Policy without
unsafe-inlineandunsafe-evalscript-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 [email protected]
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | bleach | all versions | 3.1.1pip install --upgrade 'bleach==3.1.1' |
Affected Products
fedorafedoraprojectbleachmozillaResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for bleach, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update bleach to 3.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-q65m-pv3f-wr5r is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Frequently Asked Questions
Is GHSA-q65m-pv3f-wr5r in your dependencies?
Find it across PyPI, including transitive dependencies.