{"id":"CVE-2021-28957","url":"https://www.cyber-defence.io/tools/cve/CVE-2021-28957","generatedAt":"2026-10-27T20:22:16.592Z","title":"An XSS vulnerability was discovered in python-lxml's clean module versions before 4.6.3.","description":"An XSS vulnerability was discovered in python-lxml's clean module versions before 4.6.3. When disabling the safe_attrs_only and forms arguments, the Cleaner class does not remove the formaction attribute allowing for JS to bypass the sanitizer. A remote attacker could exploit this flaw to run arbitrary JS code on users who interact with incorrectly sanitized HTML. This issue is patched in lxml 4.6.3.","published":"2021-03-21T05:15:13.000Z","lastModified":"2026-06-17T03:47:05.000Z","status":"Modified","sourceIdentifier":"cve@mitre.org","cvss":{"version":"3.1","score":6.1,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"},"cwe":["CWE-79"],"affected":["lxml/lxml","debian/debian linux","fedoraproject/fedora","netapp/snapcenter","oracle/zfs storage appliance kit"],"epss":{"score":0.04035,"percentile":0.90535,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (4.04%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"references":[{"url":"https://bugs.launchpad.net/lxml/+bug/1888153","tags":["Exploit","Issue Tracking","Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://github.com/lxml/lxml/commit/a5f9cb52079dc57477c460dbe6ba0f775e14a999","tags":["Patch","Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://github.com/lxml/lxml/pull/316/commits/10ec1b4e9f93713513a3264ed6158af22492f270","tags":["Patch","Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://lists.debian.org/debian-lts-announce/2021/03/msg00031.html","tags":["Mailing List","Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3C2R44VDUY7FJVMAVRZ2WY7XYL4SVN45/","source":"cve@mitre.org"},{"url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XXN3QPWCTQVOGW4BMWV3AUUZZ4NRZNSQ/","source":"cve@mitre.org"},{"url":"https://security.gentoo.org/glsa/202208-06","tags":["Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://security.netapp.com/advisory/ntap-20210521-0004/","tags":["Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://www.debian.org/security/2021/dsa-4880","tags":["Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://www.oracle.com/security-alerts/cpuoct2021.html","tags":["Patch","Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://bugs.launchpad.net/lxml/+bug/1888153","tags":["Exploit","Issue Tracking","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://github.com/lxml/lxml/commit/a5f9cb52079dc57477c460dbe6ba0f775e14a999","tags":["Patch","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://github.com/lxml/lxml/pull/316/commits/10ec1b4e9f93713513a3264ed6158af22492f270","tags":["Patch","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://lists.debian.org/debian-lts-announce/2021/03/msg00031.html","tags":["Mailing List","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3C2R44VDUY7FJVMAVRZ2WY7XYL4SVN45/","source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XXN3QPWCTQVOGW4BMWV3AUUZZ4NRZNSQ/","source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://security.gentoo.org/glsa/202208-06","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://security.netapp.com/advisory/ntap-20210521-0004/","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.debian.org/security/2021/dsa-4880","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.oracle.com/security-alerts/cpuoct2021.html","tags":["Patch","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2021-28957","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}