CVE-2021-32671

XSS vulnerability with translator

CRITICAL
10
CVSS Score
Published: June 7, 2021 at 09:25 PM UTC
Updated: June 17, 2026 at 03:53 AM UTC
1 product affected across 1 vendorFlarum

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Severity
CRITICAL10
Exploit prediction
EPSS 40%

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

95%
v < 1.0.21.0.01.0.1
Affected range stops below 1.0.2, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

CVSS

10CRITICALGitHub_M
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-79

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