Page defacement via unbalanced classDef CSS
Published May 22, 2026 · Updated May 22, 2026
CSS injection in Mermaid 10.9.5 and earlier and 11.0.0-alpha.1 through 11.14.0 allows remote attackers to alter rendered pages. The state diagram parser accepts an unrestricted classDef style value, which addStyleClass passes to createCssStyles and assigns to style.innerHTML; a closing brace escapes the generated selector. Exploitation requires attacker-controlled diagram text to be rendered outside sandbox mode and permits page defacement, URL-based tracking, and DOM attribute exfiltration.
Summary
What happened
CSS injection in Mermaid 10.9.5 and earlier and 11.0.0-alpha.1 through 11.14.0 allows remote attackers to alter rendered pages. The state diagram parser accepts an unrestricted classDef style value, which addStyleClass passes to createCssStyles and assigns to style.innerHTML; a closing brace escapes the generated selector. Exploitation requires attacker-controlled diagram text to be rendered outside sandbox mode and permits page defacement, URL-based tracking, and DOM attribute exfiltration.
The record
- CVE
- CVE-2026-41148
- Published
- May 22, 2026
- Updated
- May 22, 2026
- Vendor
- Mermaid
- Product
- Mermaid
- Classifications
- CWE-94
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 22, 2026CVE publishedPublication date reported by the CVE source.
- May 22, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 10.9.6
- Affected versionversion=>= 11.0.0-alpha.1, < 11.15.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- GHSA-xcj9-5m2h-648r classDef proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
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