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Cross site scripting in the system log

Moderate severity GitHub Reviewed Published Jun 23, 2021 in contao/contao • Updated Apr 17, 2025

Package

composer contao/contao (Composer)

Affected versions

>= 4.5.0, < 4.9.16
>= 4.10.0, < 4.11.5

Patched versions

4.9.16
4.11.5
composer contao/core-bundle (Composer)
>= 4.5.0, < 4.9.16
>= 4.10.0, < 4.11.5
4.9.16
4.11.5

Description

Impact

It is possible to inject code into the tl_log table that will be executed in the browser when the system log is called in the back end.

Patches

Update to Contao 4.9.16 or 4.11.5.

Workarounds

Disable the system log module in the back end for all users (especially admin users).

References

https://contao.org/en/security-advisories/cross-site-scripting-in-the-system-log-2021

For more information

If you have any questions or comments about this advisory, open an issue in contao/contao.

References

@leofeyer leofeyer published to contao/contao Jun 23, 2021
Published by the National Vulnerability Database Jun 23, 2021
Reviewed Jun 23, 2021
Published to the GitHub Advisory Database Jul 1, 2021
Last updated Apr 17, 2025

Severity

Moderate

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
Low
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:L/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(54th percentile)

Weaknesses

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

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Learn more on MITRE.

CVE ID

CVE-2021-35210

GHSA ID

GHSA-h58v-c6rf-g9f7

Source code

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