CVE-2021-32671
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedFlarum is a forum software for building communities. 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. All Flarum communities that run flarum v1.0.0 or v1.0.1 are impacted. 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceFlarum's translation system failed to properly sanitize user input, allowing malicious HTML/JavaScript to be rendered as DOM nodes in client browsers. This stored XSS vulnerability in the search box and potentially other input fields enabled attackers to execute arbitrary JavaScript in victim browsers, potentially performing AJAX actions like deleting discussions or modifying admin settings.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data= 1.0.0= 1.0.1CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed Flarum version via admin panelLog in to the Flarum admin dashboard and navigate to the Extensions page or the version info area. The current Flarum version is typically displayed in the footer or system information section.Affected if The displayed version shows exactly 1.0.0 or 1.0.1
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Check Flarum core version via composerRun `composer show flarum/core` in the Flarum installation directory to retrieve the installed core package version.Affected if The reported version of flarum/core is 1.0.0 or 1.0.1
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Check composer.json for exact versionOpen the composer.json file in the Flarum root directory and examine the flarum/core entry under require to identify the pinned version number.Affected if The flarum/core version constraint resolves to exactly 1.0.0 or 1.0.1
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Check for XSS payload in translation data (optional forensic check)Review database tables related to translations or custom translations that may contain stored malicious scripts. Examine flarum_translations or similar tables for unescaped HTML/JavaScript content.Affected if Malicious HTML or JavaScript code is found stored in translation-related database records
A Flarum installation is affected if it is running version 1.0.0 or 1.0.1 of Flarum core, as these versions contain the unsanitized translation system vulnerable to stored XSS.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade Flarum installations from v1.0.0/v1.0.1 to flarum/core v1.0.2 or later to patch the translation system's inadequate input sanitization.
flarum/core v1.0.2
- Backup your Flarum installation and database before upgrading
- Run 'composer update flarum/core' to update Flarum core to the latest version
- Alternatively, manually update composer.json to require "flarum/core": "^1.0.2" and run 'composer update'
- Clear the Flarum cache using 'php flarum cache:clear'
- Verify the installation is working correctly after upgrade
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-32671 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-32671 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data