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  5. CVE-2021-35955

CVE-2021-35955: Cross site scripting via HTML attributes in the back end

August 25, 2021 (updated April 17, 2025)

It is possible for untrusted users to inject malicious code into HTML attributes in the back end, which will be executed both in the element preview (back end) and on the website (front end).

Installations are only affected if there are untrusted back end users who have the rights to modify HTML fields (e.g. TinyMCE).

References

  • contao.org/en/news/contao-4-9-16-and-4-11-5-are-available.html
  • contao.org/en/security-advisories/cross-site-scripting-via-html-attributes-in-the-back-end.html
  • github.com/FriendsOfPHP/security-advisories/blob/master/contao/contao/CVE-2021-35955.yaml
  • github.com/FriendsOfPHP/security-advisories/blob/master/contao/core-bundle/CVE-2021-35955.yaml
  • github.com/advisories/GHSA-hr3h-x6gq-rqcp
  • github.com/contao/contao
  • github.com/contao/contao/security/advisories/GHSA-hr3h-x6gq-rqcp
  • nvd.nist.gov/vuln/detail/CVE-2021-35955

Code Behaviors & Features

Detect and mitigate CVE-2021-35955 with GitLab Dependency Scanning

Secure your software supply chain by verifying that all open source dependencies used in your projects contain no disclosed vulnerabilities. Learn more about Dependency Scanning →

Affected versions

All versions starting from 4.0.0 before 4.4.56, all versions starting from 4.5.0 before 4.9.18, all versions starting from 4.10.0 before 4.11.7

Fixed versions

  • 4.4.56
  • 4.9.18
  • 4.11.7

Solution

Upgrade to versions 4.11.7, 4.4.56, 4.9.18 or above.

Impact 4.8 MEDIUM

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

Learn more about CVSS

Weakness

  • CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Source file

packagist/contao/contao/CVE-2021-35955.yml

Spotted a mistake? Edit the file on GitLab.

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