Cross-Site Scripting (XSS) in flarum/sticky (CVE-2021-21283)
Summary
Cross-site scripting in flarum/sticky (CVE-2021-21283). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 0.1.0-beta.15.1 or later.
Original description
The description as published by the source.
Flarum is an open source discussion platform for websites. The "Flarum Sticky" extension versions 0.1.0-beta.14 and 0.1.0-beta.15 has a cross-site scripting vulnerability. A change in release beta 14 of the Sticky extension caused the plain text content of the first post of a pinned discussion to be injected as HTML on the discussion list. The issue was discovered following an internal audit. Any HTML would be injected through the m.trust() helper. This resulted in an HTML injection where tags would not be executed. However it was possible to run javascript from other HTML attributes, enabling a cross-site scripting (XSS) attack to be performed. Since the exploit only happens with the first post of a pinned discussion, an attacker would need the ability to pin their own discussion, or be able to edit a discussion that was previously pinned. On forums where all pinned posts are authored by your staff, you can be relatively certain the vulnerability has not been exploited. Forums where some user-created discussions were pinned can look at the first post edit date to find whether the vulnerability might have been exploited. Because Flarum doesn't store the post content history, you cannot be certain if a malicious edit was reverted. The fix will be available in version v0.1.0-beta.16 with Flarum beta 16. The fix has already been back-ported to Flarum beta 15 as version v0.1.0-beta.15.1 of the Sticky extension. Forum administrators can disable the Sticky extension until they are…
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-2021-21283 has been found in flarum/sticky.
Risk of unauthorized operations or information disclosure.
What to do: upgrade flarum/sticky to 0.1.0-beta.15.1 or later.
If unsure, ask your IT team or search "flarum/sticky CVE-2021-21283" on the vendor's site.
CVE-2021-21283 (flarum/sticky) — CWE-79
Attack vector: remote (network-reachable)
Patched: 0.1.0-beta.15.1 — 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/sticky.
Check the vendor advisory for the affected versions of flarum/sticky.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 0.1.0-beta.15.1.
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/sticky' . 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
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1Identify exposure identify
grep -r 'flarum/sticky' . | 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/sticky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/sticky to 0.1.0-beta.15.1ステージング環境で 0.1.0-beta.15.1 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。
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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 github.com
- advisory nvd.nist.gov
- patch github.com
- patch github.com
- web discuss.flarum.org
- web discuss.flarum.org