Ecosyste.ms: Advisories

Security Advisories: MDE2OlNlY3VyaXR5QWR2aXNvcnlHSFNBLW02eGYtZnE3cS04NzQz

mutation XSS via whitelisted math or svg and raw tag in Bleach

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

• 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=1621692
• https://cure53.de/fp170.pdf
• https://nvd.nist.gov/vuln/detail/CVE-2020-6816
• 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]

Permalink: https://github.com/advisories/GHSA-m6xf-fq7q-8743
JSON: https://advisories.ecosyste.ms/api/v1/advisories/MDE2OlNlY3VyaXR5QWR2aXNvcnlHSFNBLW02eGYtZnE3cS04NzQz
Source: GitHub Advisory Database
Origin: Unspecified
Severity: Moderate
Classification: General
Published: about 4 years ago
Updated: over 1 year ago

CVSS Score: 6.1
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Identifiers: GHSA-m6xf-fq7q-8743, CVE-2020-6816
References:

• https://github.com/mozilla/bleach/security/advisories/GHSA-m6xf-fq7q-8743
• https://github.com/mozilla/bleach/releases/tag/v3.1.2
• https://nvd.nist.gov/vuln/detail/CVE-2020-6816
• https://www.checkmarx.com/blog/vulnerabilities-discovered-in-mozilla-bleach
• https://lists.fedoraproject.org/archives/list/[email protected]/message/EDQU2SZLZMSSACCBUBJ6NOSRNNBDYFW5/
• https://advisory.checkmarx.net/advisory/CX-2020-4277
• https://github.com/advisories/GHSA-m6xf-fq7q-8743

Repository: https://github.com/mozilla/bleach
Blast Radius: 29.7

Affected Packages