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GHSA-5qjq-69w6-fg57

CriticalCVSS 10 / 10
Published Jun 7, 2021·Last modified Mar 13, 2026
Affected Components(0)

No affected components available

Description

Flarum's translation system allowed for string inputs to be converted into HTML DOM nodes when rendered. This change was made after v0.1.0-beta.16 (our last beta before v1.0.0) and was not noticed or documented.

This allowed for any user to type malicious HTML markup within certain user input fields and have this execute on client browsers. The example which led to the discovery of this vulnerability was in the forum search box. Entering faux-malicious HTML markup, such as <script>alert('test')</script> resulted in an alert box appearing on the forum. This attack could also be modified to perform AJAX requests on behalf of a user, possibly deleting discussions, modifying their settings or profile, or even modifying settings on the Admin panel if the attack was targetted towards a privileged user.

Impact

All Flarum communities that run flarum v1.0.0 or v1.0.1 are impacted.

Patches

The vulnerability has been fixed and published as flarum/core v1.0.2. All communities running Flarum v1.0 have to upgrade as soon as possible to v1.0.2 using:

composer update --prefer-dist --no-dev -a -W

You can then confirm you run the latest version using:

composer show flarum/core

Workarounds

None.

For more information

For any questions or comments on this vulnerability please visit https://discuss.flarum.org/d/27558.

For support questions create a discussion at https://discuss.flarum.org/t/support.

A reminder that if you ever become aware of a security issue in Flarum, please report it to us privately by emailing security@flarum.org, and we will address it promptly.

Risk Scores
Base Score
10.0

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.

Threat Intelligence
9.1

Active exploitation in the wild has been confirmed. Immediate patching or mitigation is required.

EPSS
39.74%

The exploit probability is moderate. The vulnerability is likely to be exploited in the next 30 days.

Exploit
Not available

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

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