CVE-2026-3254Network attack vector

Browser content injection via Mermaid sandbox validation

Published Apr 22, 2026 · Updated Apr 22, 2026

Improper frame restriction in GitLab 18.11 before 18.11.1 allows remote authenticated users to load unauthorized browser content. GitLab identifies improper input validation in the Mermaid sandbox but has not published the affected function or precise validation failure. Exploitation requires an authenticated account, network access, and interaction by another user; the published consequence is limited to browser-content integrity.

CVSS severity3.5
Low
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper frame restriction in GitLab 18.11 before 18.11.1 allows remote authenticated users to load unauthorized browser content. GitLab identifies improper input validation in the Mermaid sandbox but has not published the affected function or precise validation failure. Exploitation requires an authenticated account, network access, and interaction by another user; the published consequence is limited to browser-content integrity.

The record

CVE
CVE-2026-3254
Published
Apr 22, 2026
Updated
Apr 22, 2026
Vendor
GitLab
Product
GitLab
Classifications
CWE-1021
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 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.

  1. Affected versionversion=18.11 <18.11.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

GitLab · GitLabversion=18.11 <18.11.1

Published CVSS scores

3.5GitLab Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N

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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1021Improper Restriction of Rendered UI Layers or Frames

Public exploit references

No public exploit references are available in this record.

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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