XSS vulnerability with translator

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2021-32671: 40.00% estimated exploitation activity in the next 30 days; percentile 98.63 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 <scriptalert('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…

Published by the source

7 Jun 2021, 21:48 UTC

Last modified by the source

1 Feb 2023, 05:05 UTC

Source last checked

26 Oct 2026, 14:01 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-5qjq-69w6-fg57

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# Patch Next advisory brief: CVE-2021-32671

Advisory: XSS vulnerability with translator
IDs: CVE-2021-32671, GHSA-5qjq-69w6-fg57
Record: https://patchnext.com/advisories/cve-2021-32671 (revision 1, source checked 26 Oct 2026, 14:01 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 10.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: flarum/core 1.0.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist flarum/core: affected >= 1.0.0, <= 1.0.1; fixed in 1.0.2

## Suggested inspection (read-only)
- Packagist flarum/core: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on flarum/core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-5qjq-69w6-fg57 (GitHub-reviewed advisory GHSA-5qjq-69w6-fg57 lists affected ranges: Packagist flarum/core >=1.0.0 <=1.0.1)

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