Vulnerability CVE-2021-28957
Published: 2021-03-21

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.

Type:

CWE-79

 (Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'))

CVSS2 => (AV:N/AC:M/Au:N/C:N/I:P/A:N)

CVSS Base Score
Impact Subscore
Exploitability Subscore
4.3/10
2.9/10
8.6/10
Exploit range
Attack complexity
Authentication
Remote
Medium
No required
Confidentiality impact
Integrity impact
Availability impact
None
Partial
None
Affected software
LXML -> LXML 

 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
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