Ecosyste.ms: Advisories

Security Advisories: MDE2OlNlY3VyaXR5QWR2aXNvcnlHSFNBLXZxaHAtY3hnYy02d21t

regular expression denial-of-service (ReDoS) in Bleach

Impact

bleach.clean behavior parsing style attributes could result in a regular expression denial of service (ReDoS).

Calls to bleach.clean with an allowed tag with an allowed style attribute are vulnerable to ReDoS. For example, bleach.clean(..., attributes={'a': ['style']}).

Patches

3.1.4

Workarounds

• do not whitelist the style attribute in bleach.clean calls

• limit input string length

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1623633
• https://www.regular-expressions.info/redos.html
• https://blog.r2c.dev/posts/finding-python-redos-bugs-at-scale-using-dlint-and-r2c/
• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-6817

Credits

• Reported by schwag09 of r2c

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-vqhp-cxgc-6wmm
JSON: https://advisories.ecosyste.ms/api/v1/advisories/MDE2OlNlY3VyaXR5QWR2aXNvcnlHSFNBLXZxaHAtY3hnYy02d21t
Source: GitHub Advisory Database
Origin: Unspecified
Severity: High
Classification: General
Published: about 4 years ago
Updated: about 1 year ago

CVSS Score: 7.5
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Identifiers: GHSA-vqhp-cxgc-6wmm, CVE-2020-6817
References:

• https://github.com/mozilla/bleach/security/advisories/GHSA-vqhp-cxgc-6wmm
• https://bugzilla.mozilla.org/show_bug.cgi?id=1623633
• https://github.com/mozilla/bleach/releases/tag/v3.1.4
• https://nvd.nist.gov/vuln/detail/CVE-2020-6817
• https://snyk.io/vuln/SNYK-PYTHON-BLEACH-561754
• https://github.com/advisories/GHSA-vqhp-cxgc-6wmm

Repository: https://github.com/mozilla/bleach
Blast Radius: 36.6

Affected Packages