{"id":"CVE-2021-28957","aliases":["GHSA-jq4v-f5q6-mjqq","PYSEC-2021-19"],"url":"https://o3.security/vulnerability/CVE-2021-28957","summary":"lxml vulnerable to Cross-Site Scripting ","details":"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":"2021-03-21T05:15:13.367Z","modified":"2026-07-08T06:02:32.913857882Z","cvss":{"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"},"epss":null,"cisaKev":null,"exploitsKnown":1,"affectedPackages":[{"ecosystem":"PyPI","name":"lxml","fixedVersion":"4.6.3"}],"fix":{"url":"https://github.com/lxml/lxml/commit/a5f9cb52079dc57477c460dbe6ba0f775e14a999","label":"lxml/lxml@a5f9cb5"},"references":[{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3C2R44VDUY7FJVMAVRZ2WY7XYL4SVN45/"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XXN3QPWCTQVOGW4BMWV3AUUZZ4NRZNSQ/"},{"type":"ADVISORY","url":"https://lists.debian.org/debian-lts-announce/2021/03/msg00031.html"},{"type":"ADVISORY","url":"https://security.gentoo.org/glsa/202208-06"},{"type":"ADVISORY","url":"https://security.netapp.com/advisory/ntap-20210521-0004/"},{"type":"ADVISORY","url":"https://www.debian.org/security/2021/dsa-4880"},{"type":"REPORT","url":"https://bugs.launchpad.net/lxml/+bug/1888153"},{"type":"FIX","url":"https://github.com/lxml/lxml/commit/a5f9cb52079dc57477c460dbe6ba0f775e14a999"},{"type":"FIX","url":"https://github.com/lxml/lxml/pull/316/commits/10ec1b4e9f93713513a3264ed6158af22492f270"},{"type":"FIX","url":"https://www.oracle.com/security-alerts/cpuoct2021.html"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-08T06:02:32.913857882Z"}}