CVE-2021-32671
Flarum's translation system allowed for string inputs to be converted into HTML DOM nodes when rendered.
Does this matter?
EPSS puts the probability of exploitation in the next 30 days at 40.0%, higher than 99% of all known CVEs. Patch or mitigate before the next change window.
Description
Flarum 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.
- CVSS 3.1
- 10.0 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
- EPSS
- 40.00% probability · 99th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-79
- Affected
- flarum/flarum
- Source
- security-advisories@github.com
EPSS 40.0% since 26 October 2026; no change recorded yet. The dashed line is the ten per cent mark our analysts treat as “patch before the next change window”. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://github.com/flarum/core/commit/440bed81b8019dff00642c8f493b4909d505a28aPatch, Third Party Advisory
- https://github.com/flarum/core/security/advisories/GHSA-5qjq-69w6-fg57Third Party Advisory
- https://packagist.org/packages/flarum/coreProduct, Third Party Advisory
- https://github.com/flarum/core/commit/440bed81b8019dff00642c8f493b4909d505a28aPatch, Third Party Advisory
- https://github.com/flarum/core/security/advisories/GHSA-5qjq-69w6-fg57Third Party Advisory
- https://packagist.org/packages/flarum/coreProduct, Third Party Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.