Vulnerability in Zulip (CVE-2026-40300)
Summary
Vulnerability in Zulip (CVE-2026-40300). Confidential information can be exposed externally. Mitigation: upgrade to 12.0 or later.
Original description
The description as published by the source.
Zulip is an open-source team collaboration tool. Prior to 12.0, With message_edit_history_visibility_policy set to "moves", /api/v1/messages/{id}/history still returns historical content values, allowing low-privilege users to recover text that was edited away from other users' messages. This vulnerability is fixed in 12.0.
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-2026-40300 has been found in Zulip.
Confidential information can be exposed externally. CVSS score: 6.5/10.
What to do: upgrade Zulip to 12.0 or later.
If unsure, ask your IT team or search "Zulip CVE-2026-40300" on the vendor's site.
CVE-2026-40300 (Zulip) — CWE-284 / CVSS v3 6.5
Attack vector: remote (network-reachable) / no user interaction
Patched: 12.0 — 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.
A vulnerability (CWE-284) exists in Zulip.
Check the vendor advisory for the affected versions of Zulip.
Severity: Medium (CVSS 6.5/10). Confidential information can be exposed externally.
Update to 12.0.
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 'Zulip' . 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 'Zulip' . | 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
Zulip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 Zulip to 12.0ステージング環境で 12.0 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。
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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。
References
- advisory github.com
- advisory github.com
- advisory nvd.nist.gov