CVE-2026-50159Public exploitNetwork attack vector

CSS injection via uncontained sibling selectors

Published Aug 6, 2026 · Updated Aug 6, 2026

CSS injection in Mermaid before 10.9.8 and 11.0.0-alpha.1 through 11.16.0 allows remote attackers to alter adjacent page elements. The compileCSS addNamespace middleware lets Stylis expand diagram-controlled sibling rules into selectors that escape the SVG subtree. Exploitation requires attacker-supplied diagram text and an SVG inserted beside other DOM elements; it enables UI redressing or CSS-based probing, not JavaScript execution.

CVSS severity5.3
Medium
EPSS probability0.61%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

CSS injection in Mermaid before 10.9.8 and 11.0.0-alpha.1 through 11.16.0 allows remote attackers to alter adjacent page elements. The compileCSS addNamespace middleware lets Stylis expand diagram-controlled sibling rules into selectors that escape the SVG subtree. Exploitation requires attacker-supplied diagram text and an SVG inserted beside other DOM elements; it enables UI redressing or CSS-based probing, not JavaScript execution.

The record

CVE
CVE-2026-50159
Published
Aug 6, 2026
Updated
Aug 6, 2026
Vendor
Mermaid
Product
Mermaid
Classifications
CWE-94, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 6, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 6, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 10.9.8
  2. Affected versionversion=>= 11.0.0-alpha.1, < 11.16.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mermaid · Mermaidversion=< 10.9.8; version=>= 11.0.0-alpha.1, < 11.16.1

Published CVSS scores

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

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-94Improper Control of Generation of Code ('Code Injection')
T1189Drive-by Compromise

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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