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GHSA-26gq-grmh-6xm6

HighCVSS 7.3 / 10
Published Feb 6, 2026·Last modified Feb 19, 2026
Affected Components(0)

No affected components available

Description

Summary

Stored XSS via mermaid diagrams due to usage of vulnerable renderer library

Details

Gogs introduced support for rendering mermaid diagrams in version 0.13.0.

Currently used version of the library mermaid 11.9.0 is vulnerable to at least two XSS scenarios with publicly available payloads

Resources: https://github.com/mermaid-js/mermaid/security/advisories/GHSA-7rqq-prvp-x9jh https://github.com/mermaid-js/mermaid/security/advisories/GHSA-8gwm-58g9-j8pw

PoC

  1. Create a markdown file eg. README.md containing following malicious mermaid diagram (payload based on CVE-2025-54880)
architecture-beta
    group api(cloud)[API]
    service db "<img src=x onerror=\"alert(document.domain)\">" [Database] in api
  1. The XSS should pop whenever either repository or file is viewed

Demo

https://github.com/user-attachments/assets/98320f62-6c1c-4254-aa61-95598c725235

Impact

The attacker can potentially achieve account takeover In a worst case scenario if the victim were an instance admin this could lead to a compromise of the entire deployment

Proposed remediation steps

  1. Upgrade to a patched version of the third party library https://github.com/mermaid-js/mermaid/releases/tag/v10.9.5
  2. Consider running mermaid using sandbox level which would mitigate impact of future potential cross-site scripting issues https://mermaid.js.org/config/usage.html#securitylevel
Risk Scores
Base Score
7.3

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs basic access or low-level privileges. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data.

Threat Intelligence
6.7

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
N/A

Probability that this vulnerability will be exploited in the wild within the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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High severity
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