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GHSA-hr3h-x6gq-rqcp

MediumCVSS 5.9 / 10
Published Aug 25, 2021·Last modified Mar 13, 2026
Affected Components(0)

No affected components available

Description

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.

Risk Scores
Base Score
5.9

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs high-level or administrative privileges. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data. There is a low impact on the availability of the system.

Threat Intelligence
5.4

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
N/A

Probability that this vulnerability will be exploited in the wild within the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

Related Vulnerabilities
  • CVE-2021-35955
    Alias
  • EUVD-2021-1756
    Alias

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Medium severity
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