Bug 2480858 (CVE-2026-41148)

Summary: CVE-2026-41148 mermaid: Mermaid: CSS injection vulnerability allows page defacement and information disclosure
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: cdrage, jkoehler, lphiri, rushinde
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Mermaid, a JavaScript tool used for creating diagrams. This vulnerability, identified as a CSS injection, allows a remote attacker to inject arbitrary CSS rules due to improper sanitization of user-controlled style strings. By exploiting an unrestricted regular expression in the state diagram parser, an attacker can terminate generated CSS selectors and create new CSS rules. This can lead to page defacement, user tracking through URL (Uniform Resource Locator) callbacks, and exfiltration of Document Object Model (DOM) attributes.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On: 2489148, 2489150, 2489155, 2489156, 2489158, 2489160, 2489162, 2489147, 2489149, 2489151, 2489152, 2489153, 2489154, 2489157, 2489159, 2489161    
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Description OSIDB Bzimport 2026-05-22 23:01:20 UTC 
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>.