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    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.

    Published:Mar 21, 2021
    Last Modified:Dec 17, 2025
    EPS:Mar 21, 2021
    EPSS Score:0.00496
    CVSS Score:6.1

    Affected Products

    Vendor
    Debian
    Product
    Debian Linux
    Vendor
    Fedoraproject
    Product
    Fedora
    Vendor
    Lxml
    Product
    Lxml
    Vendor
    Netapp
    Product
    Snapcenter
    Vendor
    Oracle
    Product
    Zfs Storage Appliance Kit
    Vendor
    Redhat
    Product
    Enterprise Linux
    Vendor
    Redhat
    Product
    Rhel Software Collections

    Exploits

    https://bugs.launchpad.net/lxml/+bug/1888153https://bugs.launchpad.net/lxml/+bug/1888153

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    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
    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://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

    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