Code Injection in mermaid (CVE-2026-41148)
Summary
Code injection in mermaid (CVE-2026-41148). Risk of unauthorized operations or information disclosure. Exploitable via classDef. 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. Versions 10.9.5 and prior, in addition to 11.0.0-alpha.1 through 11.12.0 are vulnerable to CSS injection through improper sanitization. The state diagram (and any other diagram type that routes user-controlled style strings through the createCssStyles parser) captures classDef values using an unrestricted regex that matches everything up to a newline. That value then flows unsanitized through addStyleClass() into createCssStyles() and is assigned to style.innerHTML, so a closing brace (}) in the value terminates the generated CSS selector and turns everything after it into a new CSS rule on the page. This enables page defacement, user tracking via url() callbacks, and DOM attribute exfiltration. This issue has been fixed in versions 10.9.6 and 11.15.0. If developers are unable to immediately upgrade, they can work around this issue by setting "securityLevel": "sandbox", which prevents the issue by rendering the mermaid diagram in a sandboxed .
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-2026-41148 has been found in mermaid.
Attackers can target a specific entry point like classDef over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade mermaid to 10.9.6 or later.
If unsure, ask your IT team or search "mermaid CVE-2026-41148" on the vendor's site.
CVE-2026-41148 (mermaid) — CWE-94
Attack surface: classDef / style.innerHTML
Patched: 10.9.6 — apply immediately
Workaround: Setting "securityLevel": "sandbox" will prevent this, by rendering the mermaid diagram in a sandboxed <iframe>.
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 classDef.
Check the vendor advisory for the affected versions of mermaid. Attack surface: classDef / style.innerHTML.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 10.9.6.
Workaround: Setting "securityLevel": "sandbox" will prevent this, by rendering the mermaid diagram in a sandboxed <iframe>.
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 temporary workaround mitigate
Setting [`"securityLevel": "sandbox"`](https://mermaid.js.org/config/schema-docs/config.html#securitylevel) will prevent this, by rendering the mermaid diagram in a sandboxed `<iframe>`.パッチが適用されるまでの応急処置として、Setting
"securityLevel": "sandbox"will prevent this, by rendering the mermaid diagram in a sandboxed<iframe>. を実施。回避策の副作用 (機能低下) を確認した上で。 -
3Apply 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。
-
4Post-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-2026-41148 node-mermaid
- Ubuntu UBUNTU-CVE-2026-41148 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 mermaid.js.org
- web github.com