lxml vulnerable to Cross-Site Scripting
An XSS vulnerability was discovered in the python lxml 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.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | lxml | < 4.6.3 | 4.6.3 |
References
- https://bugs.launchpad.net/lxml/+bug/1888153
- https://github.com/lxml/lxml/pull/316/commits/10ec1b4e9f93713513a3264ed6158af22492f270
- https://lists.debian.org/debian-lts-announce/2021/03/msg00031.html
- https://github.com/lxml/lxml/commit/a5f9cb52079dc57477c460dbe6ba0f775e14a999
- https://www.debian.org/security/2021/dsa-4880
- https://github.com/advisories/GHSA-jq4v-f5q6-mjqq
- https://nvd.nist.gov/vuln/detail/CVE-2021-28957
- https://github.com/lxml/lxml/pull/316
- https://github.com/lxml/lxml/commit/2d01a1ba8984e0483ce6619b972832377f208a0d
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://security.netapp.com/advisory/ntap-20210521-0004
- https://security.gentoo.org/glsa/202208-06
- https://pypi.org/project/lxml
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/XXN3QPWCTQVOGW4BMWV3AUUZZ4NRZNSQ
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/3C2R44VDUY7FJVMAVRZ2WY7XYL4SVN45
- https://github.com/pypa/advisory-database/tree/main/vulns/lxml/PYSEC-2021-19.yaml
- https://github.com/lxml/lxml
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N- Weakness (CWE)
CWE-79- Platform
- Python (PyPI)
- Package
lxml- Disclosed
- 21.03.2021
- Updated
- 11.10.2026 11:20
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2021-19 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-jq4v-f5q6-mjqq - CC BY 4.0
Vulnerability history: lxml
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 7
- First → latest
- 05.2014 04.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 1
- Medium 6
Disclosures per year
- 2017: 0
- 2018: 1
- 2019: 0
- 2020: 1
- 2021: 2
- 2022: 1
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 1
earlier: 1
-
lxml vulnerable to Cross-Site Scripting this entry
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