CVE-2021-28957

Impact

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 packages

Affected products

Weakness classification

References

• NVD record
• CVE.org record
• GitHub advisory
• 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/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XXN3QPWCTQVOGW4BMWV3AUUZZ4NRZNSQ/
• https://security.gentoo.org/glsa/202208-06
• https://security.netapp.com/advisory/ntap-20210521-0004/
• https://www.debian.org/security/2021/dsa-4880
• https://www.oracle.com/security-alerts/cpuoct2021.html
• 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://pypi.org/project/lxml
• https://github.com/pypa/advisory-database/tree/main/vulns/lxml/PYSEC-2021-19.yaml
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/3C2R44VDUY7FJVMAVRZ2WY7XYL4SVN45
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/XXN3QPWCTQVOGW4BMWV3AUUZZ4NRZNSQ
• https://security.netapp.com/advisory/ntap-20210521-0004