{"id":"GHSA-vqhp-cxgc-6wmm","summary":"regular expression denial-of-service (ReDoS) in Bleach","details":"### Impact\n\n`bleach.clean` behavior parsing style attributes could result in a regular expression denial of service (ReDoS).\n\nCalls to ``bleach.clean`` with an allowed tag with an allowed ``style`` attribute are vulnerable to ReDoS. For example, ``bleach.clean(..., attributes={'a': ['style']})``.\n\n### Patches\n\n3.1.4\n\n### Workarounds\n\n* do not whitelist the style attribute in `bleach.clean` calls\n\n* limit input string length\n\n### References\n\n* https://bugzilla.mozilla.org/show_bug.cgi?id=1623633\n* https://www.regular-expressions.info/redos.html\n* https://blog.r2c.dev/posts/finding-python-redos-bugs-at-scale-using-dlint-and-r2c/\n* https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-6817\n\n### Credits\n\n* Reported by schwag09 of r2c\n\n### For more information\nIf you have any questions or comments about this advisory:\n\n* Open an issue at https://github.com/mozilla/bleach/issues\n* Email us at security@mozilla.org","aliases":["CVE-2020-6817","PYSEC-2020-340","SNYK-PYTHON-BLEACH-561754"],"modified":"2026-05-07T05:02:11.650618109Z","published":"2020-03-30T19:45:56Z","database_specific":{"github_reviewed":true,"github_reviewed_at":"2020-03-27T19:58:38Z","nvd_published_at":"2023-02-16T22:15:00Z","cwe_ids":["CWE-1333","CWE-400"],"severity":"HIGH"},"references":[{"type":"WEB","url":"https://github.com/mozilla/bleach/security/advisories/GHSA-vqhp-cxgc-6wmm"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2020-6817"},{"type":"WEB","url":"https://bugzilla.mozilla.org/show_bug.cgi?id=1623633"},{"type":"PACKAGE","url":"https://github.com/mozilla/bleach"},{"type":"WEB","url":"https://github.com/mozilla/bleach/releases/tag/v3.1.4"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/bleach/PYSEC-2020-340.yaml"},{"type":"WEB","url":"https://snyk.io/vuln/SNYK-PYTHON-BLEACH-561754"}],"affected":[{"package":{"name":"bleach","ecosystem":"PyPI","purl":"pkg:pypi/bleach"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.4"}]}],"versions":["0.1","0.1.1","0.1.2","0.2","0.2.1","0.2.2","0.3","0.3.1","0.3.3","0.3.4","0.5.0","0.5.1","1.0.0","1.0.1","1.0.2","1.0.3","1.0.4","1.1.0","1.1.1","1.1.2","1.1.3","1.1.4","1.1.5","1.2","1.2.1","1.2.2","1.4","1.4.1","1.4.2","1.4.3","1.5.0","2.0.0","2.1","2.1.1","2.1.2","2.1.3","2.1.4","3.0.0","3.0.1","3.0.2","3.1.0","3.1.1","3.1.2","3.1.3"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2020/03/GHSA-vqhp-cxgc-6wmm/GHSA-vqhp-cxgc-6wmm.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"}]}