Code Injection in mermaid (CVE-2026-50159)
Summary
Code injection in mermaid (CVE-2026-50159). Risk of unauthorized operations or information disclosure. Exploitable via secure. Mitigation: upgrade to 10.9.8 or later.
Original description
The description as published by the source.
Summary
Mermaid does not fully restrict CSS to the rendered SVG subtree. Although selectors are prefixed with #mermaid-X, sibling (~ and +) combinators can still escape the Mermaid container and inject styles to DOM elements adjacent to the diagram ``.
Most users of mermaid would not be affected by this, as mermaid adds its as an only child of it's parent element. However, you may be affected if you manually insert the (or other elements) into the DOM yourself.
Details
Mermaid namespaces CSS through with a middleware intended to scope all rules to the diagram's SVG element. CSS nesting expands & ~ * { ... } to #svgId ~ *, which selects all sibling elements following the SVG in the DOM, outside the diagram boundary.
Impact
An attacker able to supply diagram source to a page (e.g., user-generated content rendered by Mermaid) could inject CSS rules affecting sibling elements to the diagram `` on the host page. This can be used for UI redressing, hiding content, conditional CSS-based probing, or phishing-style visual manipulation.
JavaScript execution is not possible via this vector.
Patches
This has been patched in https://github.com/mermaid-js/mermaid/commit/12d472c9ed43f94814b110da8d7a9ae6dd5266ed and released in Mermaid v11.16.1.
A backport has been made for the v10 branch in 7e83f1533318b307764d961906a73377266f4c5e and was released in [Mermaid v10.9.8](https:…
Source: GitHub Security Advisories (Global) 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-2026-50159 has been found in mermaid.
Attackers can target a specific entry point like secure over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade mermaid to 10.9.8 or later.
If unsure, ask your IT team or search "mermaid CVE-2026-50159" on the vendor's site.
CVE-2026-50159 (mermaid) — CWE-94
Attack surface: secure / fontFamily / themeCSS / altFontFamily
Patched: 10.9.8 — 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.
Arbitrary code execution (CWE-94) exists in mermaid. Attackers reach the vulnerable code path via secure.
Check the vendor advisory for the affected versions of mermaid. Attack surface: secure / fontFamily / themeCSS / altFontFamily.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 10.9.8.
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 'mermaid' . 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 'mermaid' . | 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
mermaid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 mermaid to 10.9.8ステージング環境で 10.9.8 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
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-50159 node-mermaid
- Ubuntu UBUNTU-CVE-2026-50159 node-mermaid