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lxml's HTML Cleaner allows crafted and SVG embedded scripts to pass through

High severity GitHub Reviewed Published Dec 12, 2021 in lxml/lxml • Updated Jan 30, 2023

Package

pip lxml (pip)

Affected versions

< 4.6.5

Patched versions

4.6.5

Description

Impact

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.

Patches

The issue has been resolved in lxml 4.6.5.

Workarounds

None.

References

The issues are tracked under the report IDs GHSL-2021-1037 and GHSL-2021-1038.

References

@scoder scoder published to lxml/lxml Dec 12, 2021
Reviewed Dec 13, 2021
Published to the GitHub Advisory Database Dec 13, 2021
Published by the National Vulnerability Database Dec 13, 2021
Last updated Jan 30, 2023

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:N

EPSS score

0.680%
(80th percentile)

Weaknesses

CVE ID

CVE-2021-43818

GHSA ID

GHSA-55x5-fj6c-h6m8

Source code

Credits

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