CVE-2026-41148
mediumpriority · track · 0EPSS 0.003 · 27 %ileEUUSEPSS · scored 2026-10-27
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 <iframe>.
cvss
Technical severity, 0–10. One row per scoring source.
base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · low–medium · 1.3–5.3
ssvc
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weaknesses
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affected products (4)
Products and version ranges known to be affected.
advisories (1)
Vendor and ecosystem advisories describing this.
- GHSA-xcj9-5m2h-648rMermaid: Improper sanitization of `classDefs` in diagrams leads to CSS injection2026-05-11ghsa · osvUS
### Details The state diagram and any other diagram type that routes user-controlled style strings through createCssStyles parser for Mermaid v11.14.0 and earlier captures `classDef` values with an unrestricted regex: ```jison // packages/mermaid/src/diagrams/state/parser/stateDiagram.jison:83 <CLASSDEFID>[^\n]* { this.popState(); return 'CLASSDEF_STYLEOPTS' } ``` The value passes unsanitized through `addStyleClass()` -> `createCssStyles()` -> `style.innerHTML` (mermaidAPI.ts:418). A `}` in the value closes the generated CSS selector, and everything after becomes a new CSS rule on the page. ### PoC ``` stateDiagram-v2 classDef x }*{ background-image: url("http://media.giphy.com/media/SggILpMXO7Xt6/giphy.gif")} ``` Live demo: <https://mermaid.live/edit#pako:eNpFjzFvgzAQhf-KdVNbEcBgMHhtlkqtOnSJKi8ONsYKBmRMlRTx3-skanvTfbp7996t0IxSAYPZC6_2Rmgn7O4rQ00v5nmvWnRG29OKjqI5aTcug9wZK7RiaHH9A4fO-4kliVXSiFibqbvEzWjvnHxo_fI6vR3e6cGXyX2qTcvhcYMItDMSmHeLisAqZ8UVYeUDQhx8p6ziwEIrhTtx4MNVM4nhcxztrywE0h2wVvRzoGWS_z_8rahBKvcckntgmN5OAFvhDIzUNCZZQXCR5nVaZkUEF2BVFpOcEkoxxhUuyRbB980yjStapKHqoKFlhvPtB7BFZEU> ### Patches This has been patched in: - [v11.15.0](https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0) (see [e9b0f34d8d82a6260077764ee45e1d7d90957a0f](https://github.com/mermaid-js/mermaid/commit/e9b0f34d8d82a6260077764ee45e1d7d90957a0f)) - [v10.9.6](https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6) (see [8fead23c59166b7bab6a39eac81acebee2859102](https://github.com/mermaid-js/mermaid/commit/8fead23c59166b7bab6a39eac81acebee2859102)) ### Workarounds 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>`. ### Impact Enables page defacement, user tracking via `url()` callbacks, and DOM attribute exfiltration via CSS `:has()` selectors.
also known as (3)
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sources
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references (19)
External citations — patches, advisories, analysis.
- https://github.com/mermaid-js/mermaid/commit/8fead23c59166b7bab6a39eac81acebee2859102cnnvd
- https://github.com/mermaid-js/mermaid/commit/e9b0f34d8d82a6260077764ee45e1d7d90957a0fcnnvd
- https://github.com/mermaid-js/mermaid/releasesPatchcnnvd
- https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0cnnvd
- https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6cnnvd
- https://github.com/mermaid-js/mermaid/security/advisories/GHSA-xcj9-5m2h-648rcnnvd
- https://mermaid.js.org/config/schema-docs/config.html#securitylevelcnnvd
- https://github.com/mermaid-js/mermaid/commit/8fead23c59166b7bab6a39eac81acebee2859102enisa_euvd
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