GHSA-87f9-hvmw-gh4p Mermaid: Improper sanitization of configuration leads to CSS injection

• npm mermaid: >= 11.0.0-alpha.1, < 11.15.0 → fixed in 11.15.0 • npm mermaid: < 10.9.6 → fixed in 10.9.6

Impact Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the `fontFamily`, `themeCSS`, and `altFontFamily` configuration options. Live demo: mermaid.live Example code: ``` %%{init: {"fontFamily": "x;a{b} :not(&){background:green !important} c{d}"}}%% flowchart LR A --> B ``` 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. Patches • v11.15.0 (see 64769738d5b59211e1decb471ffbaca8afec51aa) • v10.9.6 (see a9d9f0d8eb790349121508688cd338253fd80d76) Workarounds If you can't upgrade mermaid, you can set the `secure` config value in the mermaid config to avoid allowing diagrams to modify `fontFamily`, `themeCSS`, `altFontFamily`, and `themeVariables`. Setting `"securityLevel": "sandbox"` will also prevent this. Credits Reported by @zsxsoft on behalf of @KeenSecurityLab