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CVE-2026-50159

Mermaid allows CSS injection applying to sibling elements of the diagram

MEDIUM
5.3
CVSS Score
Published: August 6, 2026 at 07:55 PM UTC
Updated: October 24, 2026 at 04:10 PM UTC
1 product affected across 1 vendorMermaid

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Severity
MEDIUM5.3
Exploit prediction
EPSS 0.6%
SSVC
No known exploit

Description

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Mermaid· Mermaid Js
90%
v < 10.9.8>= 11.0.0-alpha.1, < 11.16.1
Affected range stops below 10.9.8, so it looks safe — our inference, not a vendor statement
Affected range stops below 11.16.1, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet, and no fixed version or vendor advisory is recorded against it.

References (6)

x_refsource_MISC
Source: [email protected]
https://github.com/mermaid-js/mermaid/commit/12d472c9ed43f94814b110da8d7a9ae6dd5266ed
x_refsource_MISC
Source: [email protected]
https://github.com/mermaid-js/mermaid/commit/7e83f1533318b307764d961906a73377266f4c5e
x_refsource_MISC
Source: [email protected]
https://github.com/mermaid-js/mermaid/pull/8022
x_refsource_MISC
Source: [email protected]
https://github.com/mermaid-js/mermaid/releases/tag/[email protected]
x_refsource_MISC
Source: [email protected]
https://github.com/mermaid-js/mermaid/releases/tag/v10.9.8
x_refsource_CONFIRM
Source: [email protected]
https://github.com/mermaid-js/mermaid/security/advisories/GHSA-6x64-9x62-f2gx

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.3MEDIUMGitHub_M
Vector?

Quick Info

StatusAWAITING ANALYSIS
CWE
CWE-94

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