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CVE-2021-28957

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Date: March 20, 2021

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.

Language: Python

Severity Score

Related Resources (24)

https://security.gentoo.org/glsa/202208-06
https://github.com/lxml/lxml/pull/316/commits/10ec1b4e9f93713513a3264ed6158af22492f270
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/XXN3QPWCTQVOGW4BMWV3AUUZZ4NRZNSQ
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XXN3QPWCTQVOGW4BMWV3AUUZZ4NRZNSQ/
https://security-tracker.debian.org/tracker/CVE-2021-28957
https://www.debian.org/security/2021/dsa-4880
https://lists.debian.org/debian-lts-announce/2021/03/msg00031.html
https://access.redhat.com/security/cve/CVE-2021-28957
https://github.com/lxml/lxml
https://nvd.nist.gov/vuln/detail/CVE-2021-28957
https://bugs.launchpad.net/lxml/+bug/1888153
https://security.netapp.com/advisory/ntap-20210521-0004/
https://github.com/advisories/GHSA-jq4v-f5q6-mjqq
https://pypi.org/project/lxml
https://github.com/lxml/lxml/commit/a5f9cb52079dc57477c460dbe6ba0f775e14a999
https://security.alpinelinux.org/vuln/CVE-2021-28957
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://security.netapp.com/advisory/ntap-20210521-0004
https://github.com/lxml/lxml/commit/2d01a1ba8984e0483ce6619b972832377f208a0d
https://www.oracle.com/security-alerts/cpuoct2021.html
https://github.com/lxml/lxml/pull/316
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3C2R44VDUY7FJVMAVRZ2WY7XYL4SVN45/
https://www.mend.io/vulnerability-database/CVE-2021-28957

Severity Score

Weakness Type (CWE)

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

CWE-79

Top Fix

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Upgrade Version

Upgrade to version lxml - 4.6.3

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CVSS v3.1

Base Score:
Attack Vector (AV): NETWORK
Attack Complexity (AC): LOW
Privileges Required (PR): NONE
User Interaction (UI): REQUIRED
Scope (S): CHANGED
Confidentiality (C): LOW
Integrity (I): LOW
Availability (A): NONE

CVSS v2

Base Score:
Access Vector (AV): NETWORK
Access Complexity (AC): MEDIUM
Authentication (AU): NONE
Confidentiality (C): NONE
Integrity (I): PARTIAL
Availability (A): NONE
Additional information:

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