Code Injection in mermaid (CVE-2026-41159)
Summary
Code injection in mermaid (CVE-2026-41159). Risk of unauthorized operations or information disclosure. Exploitable via fontFamily. Mitigation: upgrade to 10.9.6 or later.
Original description
The description as published by the source.
Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the fontFamily, themeCSS, and altFontFamily configuration options. The injected CSS exploits stylis's & (scope reference) handling. :not(&) escapes the #mermaid-xxx automatic scoping, applying styles to all page elements. Global at-rules (@font-face, @keyframes, @counter-style) are also injectable as stylis hoists them to top level. This allows page defacement and DOM attribute exfiltration via CSS :has() selectors. This vulnerability is fixed in 10.9.6 and 11.15.0.
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-2026-41159 has been found in mermaid.
Attackers can target a specific entry point like fontFamily over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade mermaid to 10.9.6 or later.
If unsure, ask your IT team or search "mermaid CVE-2026-41159" on the vendor's site.
CVE-2026-41159 (mermaid) — CWE-94 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: fontFamily / themeCSS / altFontFamily / secure
Patched: 10.9.6 — 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 fontFamily without authentication.
Check the vendor advisory for the affected versions of mermaid. Attack surface: fontFamily / themeCSS / altFontFamily / secure.
Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.
Update to 10.9.6.
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
-
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 10.9.6ステージング環境で 10.9.6 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-2026-41159 node-mermaid
- Ubuntu UBUNTU-CVE-2026-41159 node-mermaid
References
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- patch github.com
- patch github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com