GHSA-26gq-grmh-6xm6 Gogs vulnerable to Stored XSS via Mermaid diagrams

• Go gogs.io/gogs: < 0.13.4 → fixed in 0.13.4

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 "" [Database] in api ``` 2. 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