UBUNTU-CVE-2021-28957

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    UBUNTU-CVE-2021-28957

    Published: 21 Mar 2021Last Modified: 4 Feb 2026
    Upstream:
    CVE-2021-28957

    Summary:

    Details: 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.

    References: https://ubuntu.com/security/CVE-2021-28957, https://bugs.launchpad.net/lxml/+bug/1888153, https://github.com/lxml/lxml/pull/316, https://github.com/lxml/lxml/pull/316/commits/10ec1b4e9f93713513a3264ed6158af22492f270, https://lists.debian.org/debian-lts-announce/2021/03/msg00031.html, https://ubuntu.com/security/notices/USN-4896-1, https://ubuntu.com/security/notices/USN-4896-2, https://www.cve.org/CVERecord?id=CVE-2021-28957

    Affected packages

    Package

    Name: lxml

    Purl: pkg:deb/ubuntu/[email protected]+esm3?arch=source&distro=trusty/esm

    Affected ranges

    Type: ECOSYSTEM

    Events:

    Introduced- 0
    Fixed -3.3.3-1ubuntu0.2+esm3

    Affected versions

    3.2.0-1

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High
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