Mermaid allows CSS injection applying to sibling elements of the diagram

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.8 and 11.16.1, Mermaid is vulnerable to CSS injection via sibling combinator selectors generated from diagram-supplied class or id names. An attacker who can supply diagram text can inject arbitrary CSS into the rendered page, potentially altering the appearance or behavior of unrelated page elements. This issue is fixed in versions 10.9.8 and 11.16.1.

Source published

6 Aug 2026 19:55:27 UTC

Source modified

7 Aug 2026 17:18:23 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 5.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.8 and 11.16.1, Mermaid is vulnerable to CSS injection via sibling combinator selectors generated from diagram-supplied class or id names. An attacker who can supply diagram text can inject arbitrary CSS into the rendered page, potentially altering the appearance or behavior of unrelated page elements. This issue is fixed in versions 10.9.8 and 11.16.1.

Source published

Aug 6, 2026, 7:55:27 PM (timezone not stated)

Source modified

Aug 7, 2026, 5:18:23 PM (timezone not stated)

Observed here

7 Nov 2026 11:32:55 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 5.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.8 and 11.16.1, Mermaid is vulnerable to CSS injection via sibling combinator selectors generated from diagram-supplied class or id names. An attacker who can supply diagram text can inject arbitrary CSS into the rendered page, potentially altering the appearance or behavior of unrelated page elements. This issue is fixed in versions 10.9.8 and 11.16.1.

Source published

6 Aug 2026 22:17:17 UTC

Source modified

24 Oct 2026 16:10:00 UTC

Observed here

25 Oct 2026 12:17:38 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 5.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

### 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 `<svg>`. **Most users of mermaid would not be affected by this**, as mermaid adds its `<svg>` as an only child of it's parent element. However, you may be affected if you manually insert the `<svg>` (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 `<svg>` 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](https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.16.1). A backport has been made for the v10 branch in 7e83f1533318b307764d961906a73377266f4c5e and was released in [Mermaid v10.9.8](https://github.com/mermaid-js/mermaid/releases/tag/v10.9.8) ### Workarounds If you are inserting the `<svg>` into the DOM yourself, you can wrap it in an element with no other children, e.g. `<div><svg>...</svg></div>` or `element.innerHTML = svg`. Alternatively, you can use `mermaid.run()` or `mermaid.initialize()` which will do this for you. Setting ["securityLevel": "sandbox"](https://mermaid.js.org/config/schema-docs/config.html#securitylevel) will also prevent this, or setting the [`secure`](https://mermaid.js.org/config/schema-docs/config.html#secure) config value in the mermaid config to avoid allowing diagrams to modify `fontFamily`, `themeCSS`, `altFontFamily`, and `themeVariables`. To test, you can try using a `themeCSS` with `& + * { /* my CSS here */}` and see if it's applied outside of your mermaid `<svg>`. ```mermaid-example --- config: themeCSS: |- & + * { background:red !important; width:100vw !important; height:100vh !important; position:fixed !important; inset:0 !important; } --- info ``` ### References - GHSA-87f9-hvmw-gh4p/CVE-2026-41159 (related vulnerability) - https://github.com/mermaid-js/mermaid/commit/12d472c9ed43f94814b110da8d7a9ae6dd5266ed - https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.16.1 - https://github.com/mermaid-js/mermaid/commit/7e83f1533318b307764d961906a73377266f4c5e - https://github.com/mermaid-js/mermaid/releases/tag/v10.9.8

Source published

6 Aug 2026 19:55:31 UTC

Source modified

10 Sep 2026 03:51:13 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L

Publisher rating · MODERATE