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Medium

Cross site scripting via HTML attributes in the back end

  • Disclosed: 25.08.2021
  • Updated: 11.10.2026 10:22

Impact

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).

Patches

Update to Contao 4.4.56, 4.9.18 or 4.11.7

Workarounds

Disable all fields that allow HTML for untrusted back end users or disable the login for these users.

References

https://contao.org/en/security-advisories/cross-site-scripting-via-html-attributes-in-the-back-end

For more information

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

Credits

Thanks to Mikhail Khramenkov and Moritz Vondano for reporting this security issue.

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Composer package contao/contao >= 4.0.0, < 4.4.56, >= 4.5.0, < 4.9.18, >= 4.10.0, < 4.11.7 4.4.56, 4.9.18, 4.11.7
Composer package contao/core-bundle >= 4.0.0, < 4.4.56, >= 4.5.0, < 4.9.18, >= 4.10.0, < 4.11.7 4.4.56, 4.9.18, 4.11.7

References

CVSS score 5.9/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:L
Weakness (CWE)
CWE-79
Platform
Composer
Package
contao/contao, contao/core-bundle
Disclosed
25.08.2021
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-hr3h-x6gq-rqcp - CC BY 4.0

Vulnerability history: contao/core-bundle

All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (40) in the archive
Total entries
40
First → latest
12.2019 10.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • Critical 4
  • High 7
  • Medium 23
  • Low 6

Disclosures per year

Severity:
  1. Contao affected by remote command execution through file upload
    High · 8.3 CVE-2024-45398 >= 4.0.0, < 4.13.49, >= 5.0.0, < 5.3.15, >= 5.4.0, < 5.4.3 4.13.49, 5.3.15, 5.4.3
  2. Contao: Possible cookie sharing with external domains while checking protected pages for broken links
    High · 8.3 CVE-2024-28235 >= 4.9.0, < 4.13.40, >= 5.0.0-RC1, < 5.3.4 4.13.40, 5.3.4
  3. Contao SQL injection in the file manager
    Critical · 9.8 CVE-2019-11512 >= 4.1.0, < 4.4.39, >= 4.5.0, < 4.7.5 4.4.39, 4.7.5
  4. Contao SQL injection in the backend and listing module
    Critical · 9.8 CVE-2017-16558 >= 4.0.0, < 4.4.8, >= 3.0.0, <= 3.5.30 4.4.8
  5. Cross site scripting via canonical tag in Contao
    High · 7.2 CVE-2022-24899 >= 4.13.0, < 4.13.3 4.13.3
  6. Contao CSRF Token Bypass
    High · 8.8 CVE-2019-10642 >= 4.7.0, < 4.7.3 4.7.3
  7. Contao Does Not Invalidate Existing Sessions When Password Changes
    Critical · 9.8 CVE-2019-10641 >= 4.0.0, < 4.4.37, >= 4.5.0, < 4.7.3 4.4.37, 4.7.3
  8. Contao Core directory traversal vulnerability
    High · 8.8 CVE-2017-10993 >= 4.0.0, < 4.4.1 4.4.1
  9. Contao Does Not Expire Tokens Correctly
    Critical · 9.8 CVE-2019-10643 >= 4.7.0, < 4.7.3 4.7.3
  10. Cross site scripting via HTML attributes in the back end this entry
    Medium · 5.9 CVE-2021-35955 >= 4.0.0, < 4.4.56, >= 4.5.0, < 4.9.18, >= 4.10.0, < 4.11.7 4.4.56, 4.9.18, 4.11.7
  11. Privilege escalation via form generator
    High · 8.0 CVE-2021-37627 >= 4.0.0, < 4.4.56, >= 4.5.0, < 4.9.18, >= 4.10.0, < 4.11.7 4.4.56, 4.9.18, 4.11.7
  12. Unrestricted file uploads in Contao
    High · 8.8 CVE-2019-19745 >= 4.0.0, < 4.4.46, >= 4.5.0, < 4.8.6 4.4.46, 4.8.6

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