Security readout for executives and security teams
Plain-English summary
Flarum 1.0.0 and 1.0.1 let user-supplied text become executable HTML in client browsers through the translation rendering path. Malicious forum input, including search text, could run in another user’s browser and act with that user’s permissions. For administrators, this could affect site configuration and community integrity. Upgrade urgency is high for affected forums.
Executive priority
Treat this as urgent if the organization runs Flarum 1.0.0 or 1.0.1. The issue can let untrusted forum input run actions in users’ browsers, with severe impact if administrators are affected. No active exploitation is cited in the provided sources.
Technical view
CWE-79 cross-site scripting in flarum/core >=1.0.0 and <1.0.2: translation strings could convert user input into HTML DOM nodes when rendered. The advisory states attacker-controlled markup in certain fields could execute in browsers and perform AJAX requests as the victim, with scope change and high confidentiality, integrity, and availability impact. Fixed in flarum/core v1.0.2.
Likely exposure
Exposure is limited to Flarum communities running flarum/core v1.0.0 or v1.0.1. The bundle does not identify other affected products or extensions. Public forums are higher concern because anonymous or low-trust users may reach input fields.
Exploitation context
The source bundle does not show CISA KEV listing or confirmed active exploitation. The vendor advisory describes browser-side execution from user input and potential victim-context actions, including privileged admin effects if an administrator is targeted.
Researcher notes
The root issue is unsafe rendering in Flarum’s translation system after beta.16 and before v1.0.2. Evidence is strongest from the GitHub security advisory, CVE record, and fixing commit. The bundle does not provide broad exploitation telemetry or extension-specific exposure details.
Mitigation direction
- Upgrade affected Flarum communities to flarum/core v1.0.2 or later.
- Identify any deployments running flarum/core v1.0.0 or v1.0.1.
- Review the GitHub advisory and vendor package guidance before deploying changes.
- Prioritize administrative forums and public-facing communities first.
- Review the affected period for unexpected profile, discussion, or admin setting changes.
Validation and detection
- Check deployed flarum/core package versions against >=1.0.0 and <1.0.2.
- Confirm production and staging forums report flarum/core v1.0.2 or later.
- Verify dependency lockfiles and deployment artifacts no longer reference affected versions.
- Review forum audit logs for unusual administrative or account changes.
- Document affected instances, upgrade timing, and residual monitoring actions.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-79: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-32671 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 10 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H3.96Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
10CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/flarum/core/security/advisories/GHSA-5qjq-69w6-fg57CVE reference · x_refsource_CONFIRM
- https://github.com/flarum/core/commit/440bed81b8019dff00642c8f493b4909d505a28aCVE reference · x_refsource_MISC
- https://packagist.org/packages/flarum/coreCVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.