XSS in Lxml
CVE-2021-28957
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.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.040 (90.5th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 90th percentile — 90.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.040 · newest: 0.040 · change: 0.000
Affected products
- Lxml
- NetApp Snapcenter
- Oracle Zfs Storage Appliance Kit — versions 8.8
- Debian Linux — versions 9.0, 10.0
- Fedoraproject Fedora — versions 33, 34
Weakness classification (CWE)
Public proof-of-concept exploits
References
- bugs.launchpad.net/lxml/+bug/1888153 (Exploit, Third Party Advisory, Issue Tracking)
- github.com/lxml/lxml/pull/316/commits/10ec1b4e9f93713513a3264ed6158af22492f270 (Patch, Third Party Advisory)
- lists.debian.org/debian-lts-announce/2021/03/msg00031.html (mailing-list, Mailing List, Third Party Advisory)
- www.debian.org/security/2021/dsa-4880 (vendor-advisory, Third Party Advisory)
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)
- www.oracle.com/security-alerts/cpuoct2021.html (Patch, Third Party Advisory)
- github.com/lxml/lxml/commit/a5f9cb52079dc57477c460dbe6ba0f775e14a999 (Patch, Third Party Advisory)
- security.netapp.com/advisory/ntap-20210521-0004/ (Third Party Advisory)
- security.gentoo.org/glsa/202208-06 (vendor-advisory, Third Party Advisory)
Frequently asked questions
- What is CVE-2021-28957?
- CVE-2021-28957 is a medium-severity vulnerability in Lxml, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-03-21.
- How severe is CVE-2021-28957?
- Medium severity. CVSS v3 base score is 6.1 out of 10.
- Is CVE-2021-28957 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.