CVE-2021-43818 - CVE House
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Status published High CVE-2021-43818

HTML Cleaner allows crafted and SVG embedded scripts to pass through

Vulnerability Description

lxml is a library for processing XML and HTML in the Python language. Prior to version 4.6.5, the HTML Cleaner in lxml.html lets certain crafted script content pass through, as well as script content in SVG files embedded using data URIs. Users that employ the HTML cleaner in a security relevant context should upgrade to lxml 4.6.5 to receive a patch. There are no known workarounds available.

Impact Analysis

Refer to official advisory for detailed impact metrics.

Remediation

Ensure systems are updated to the latest vendor-supplied patch levels.

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Credits & Attribution

No credits recorded in the NVD database.

References

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CVE-2018-19787
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CVE-2014-3146
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Affected Vendor

Affected Software

lxml
Vulnerable Versions:
< 4.6.5

Timeline

Official Publish: December 13th, 2021
Last Modified: December 18th, 2025
Added to House: July 21st, 2026

CVSS Vectors

V3: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:N

Weaknesses (CWE)

CWE-74 CWE-79

MITRE ATT&CK TTPs

T1190 Exploit Public-Facing Application
Initial Access
T1059 Command and Scripting Interpreter
Execution
T1562 Impair Defenses
Defense Evasion
T1213 Data from Information Repositories
Collection
T1189 Drive-by Compromise
Initial Access
T1059.007 JavaScript
Execution
T1539 Steal Web Session Cookie
Collection
T1567 Exfiltration Over Web Service
Exfiltration
T1491.001 Defacement
Impact