Cross-Site Scripting (XSS) in flarum/core (CVE-2021-32671)
Summary
Cross-site scripting in flarum/core (CVE-2021-32671). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 1.0.2 or later.
Original description
The description as published by the source.
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 alert('test') 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 have to upgrade as soon as possible to v1.0.2 using:
composer update --prefer-dist --no-dev -a -W
You can then confirm you run the latest version using:
composer show flarum/core
Workarounds
None.
For more information
For any questions or comments on this vulnerability please visit https://discuss.flarum.org/d/27558.
For support questions create a discussion at https://discuss.flarum.org/t/support.
A reminder that if you ever become aware of a security issue in Fl…
Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2021-32671 has been found in flarum/core.
Successful exploitation can lead to full system takeover.
What to do: upgrade flarum/core to 1.0.2 or later.
If unsure, ask your IT team or search "flarum/core CVE-2021-32671" on the vendor's site.
CVE-2021-32671 (flarum/core) — CWE-79
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 1.0.2 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Cross-site scripting (XSS) (CWE-79) exists in flarum/core.
Check the vendor advisory for the affected versions of flarum/core.
Severity: ?. Successful exploitation can lead to full system takeover.
Update to 1.0.2.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'flarum/core' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'flarum/core' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
flarum/coreを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade flarum/core to 1.0.2ステージング環境で 1.0.2 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- web github.com
- web github.com
- web packagist.org