OS Command Injection in Discourse (CVE-2026-55420)
Summary
OS command injection in Discourse (CVE-2026-55420). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 2026.6.0 or later.
Original description
The description as published by the source.
Discourse is an open-source discussion platform. Prior to 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, under certain non-default configurations, processing of PDF uploads could be exploited to obtain RCE on the server. This issue is patched in 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5.
Source: NIST National Vulnerability Database NVD GitHub Advisory
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-2026-55420 has been found in Discourse.
Successful exploitation can lead to full system takeover. CVSS score: 7.5/10.
What to do: upgrade Discourse to 2026.6.0 or later.
If unsure, ask your IT team or search "Discourse CVE-2026-55420" on the vendor's site.
CVE-2026-55420 (Discourse) — CWE-78 / CVSS v3 7.5
Attack vector: remote (network-reachable) / no user interaction
Patched: 2026.6.0 — 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.
OS command injection (CWE-78) exists in Discourse.
Check the vendor advisory for the affected versions of Discourse.
Severity: High (CVSS 7.5/10). Successful exploitation can lead to full system takeover.
Update to 2026.6.0.
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 'Discourse' . 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 'Discourse' . | 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
Discourse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 Discourse to 2026.6.0ステージング環境で 2026.6.0 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 github.com
- patch github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web nvd.nist.gov