{"cve":"CVE-2021-28957","nvd":{"published":"2021-03-21T05:15:13.367","modified":"2026-06-17T03:47:04.717","status":"Modified","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","score":6.1},"cwes":["CWE-79"],"references":["https://bugs.launchpad.net/lxml/+bug/1888153","https://github.com/lxml/lxml/commit/a5f9cb52079dc57477c460dbe6ba0f775e14a999","https://github.com/lxml/lxml/pull/316/commits/10ec1b4e9f93713513a3264ed6158af22492f270","https://lists.debian.org/debian-lts-announce/2021/03/msg00031.html","https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3C2R44VDUY7FJVMAVRZ2WY7XYL4SVN45/"],"products":["debian:debian_linux","fedoraproject:fedora","lxml:lxml","netapp:snapcenter","oracle:zfs_storage_appliance_kit"],"source":"nvd","synced_at":"2026-10-19T21:15:50.279857260+00:00"},"epss":{"cve":"CVE-2021-28957","score":0.04035,"percentile":0.90607,"date":"2026-11-01"},"kev":null,"osv":[{"id":"GHSA-jq4v-f5q6-mjqq","url":"https://osv.dev/vulnerability/GHSA-jq4v-f5q6-mjqq","summary":"lxml vulnerable to Cross-Site Scripting ","modified":"2024-09-30T17:01:18.596416Z","packages":[{"ecosystem":"PyPI","name":"lxml","purl":"pkg:pypi/lxml","ranges":["<4.6.3"],"fixed":["4.6.3"]}]},{"id":"PYSEC-2021-19","url":"https://osv.dev/vulnerability/PYSEC-2021-19","summary":"","modified":"2023-11-08T04:05:32.182293Z","packages":[{"ecosystem":"PyPI","name":"lxml","purl":"pkg:pypi/lxml","ranges":["<4.6.3"],"fixed":["4.6.3"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}