{"id":"GHSA-26gq-grmh-6xm6","aliases":["GO-2026-4454"],"status":"published","title":"Gogs vulnerable to Stored XSS via Mermaid diagrams","description":"### Summary\nStored XSS via mermaid diagrams due to usage of vulnerable renderer library\n\n### Details\nGogs introduced support for rendering mermaid diagrams in version [0.13.0.](https://github.com/gogs/gogs/releases/tag/v0.13.0)\n\nCurrently used version of the library [mermaid 11.9.0](https://github.com/gogs/gogs/tree/main/public/plugins/mermaid-11.9.0) is vulnerable to at least two XSS scenarios with publicly available payloads\n\nResources:\nhttps://github.com/mermaid-js/mermaid/security/advisories/GHSA-7rqq-prvp-x9jh\nhttps://github.com/mermaid-js/mermaid/security/advisories/GHSA-8gwm-58g9-j8pw\n\n### PoC\n\n1. Create a markdown file eg. `README.md` containing following malicious mermaid diagram (payload based on [CVE-2025-54880](https://github.com/mermaid-js/mermaid/security/advisories/GHSA-8gwm-58g9-j8pw))\n```\narchitecture-beta\n    group api(cloud)[API]\n    service db \"\u003cimg src=x onerror=\\\"alert(document.domain)\\\"\u003e\" [Database] in api\n```\n2. The XSS should pop whenever either repository or file is viewed\n\n#### Demo\n\nhttps://github.com/user-attachments/assets/98320f62-6c1c-4254-aa61-95598c725235\n\n### Impact\nThe attacker can potentially achieve account takeover\nIn a worst case scenario if the victim were an instance admin this could lead to a compromise of the entire deployment\n\n### Proposed remediation steps\n1. Upgrade to a patched version of the third party library\nhttps://github.com/mermaid-js/mermaid/releases/tag/v10.9.5\n2. Consider running mermaid using `sandbox` level which would mitigate impact of future potential cross-site scripting issues\nhttps://mermaid.js.org/config/usage.html#securitylevel","severity":{"version":"3.1","score":7.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N","level":"high","from":"ghsa"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-1395","CWE-79"],"published":"2026-02-06T19:44:14Z","modified":"2026-02-19T20:41:26Z","fixes":[{"ecosystem":"Go","package":"gogs.io/gogs","fixed_in":["0.13.4"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"Go","package":"gogs.io/gogs","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"0.13.3"},{"fixed":"0.13.4"}]}]},{"source":"osv","ecosystem":"Go","package":"gogs.io/gogs","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.13.4"}]}]},{"source":"osv","ecosystem":"Go","package":"gogs.io/gogs","ranges":[{"type":"SEMVER","events":[{"introduced":"0"}]}]}],"references":[{"url":"https://github.com/gogs/gogs/security/advisories/GHSA-26gq-grmh-6xm6","tags":["web","advisory"]},{"url":"https://github.com/mermaid-js/mermaid/security/advisories/GHSA-7rqq-prvp-x9jh","tags":["web"]},{"url":"https://github.com/mermaid-js/mermaid/security/advisories/GHSA-8gwm-58g9-j8pw","tags":["web"]},{"url":"https://github.com/gogs/gogs/commit/71a72a72ad1c8cea7940c9d7e4cbdfbc0fc3d401","tags":["web"]},{"url":"https://github.com/advisories/GHSA-26gq-grmh-6xm6"},{"url":"https://github.com/gogs/gogs","tags":["package"]}],"sources":{"ghsa":[{"id":"GHSA-26gq-grmh-6xm6","title":"Gogs vulnerable to Stored XSS via Mermaid diagrams","description":"### Summary\nStored XSS via mermaid diagrams due to usage of vulnerable renderer library\n\n### Details\nGogs introduced support for rendering mermaid diagrams in version [0.13.0.](https://github.com/gogs/gogs/releases/tag/v0.13.0)\n\nCurrently used version of the library [mermaid 11.9.0](https://github.com/gogs/gogs/tree/main/public/plugins/mermaid-11.9.0) is vulnerable to at least two XSS scenarios with publicly available payloads\n\nResources:\nhttps://github.com/mermaid-js/mermaid/security/advisories/GHSA-7rqq-prvp-x9jh\nhttps://github.com/mermaid-js/mermaid/security/advisories/GHSA-8gwm-58g9-j8pw\n\n### PoC\n\n1. Create a markdown file eg. `README.md` containing following malicious mermaid diagram (payload based on [CVE-2025-54880](https://github.com/mermaid-js/mermaid/security/advisories/GHSA-8gwm-58g9-j8pw))\n```\narchitecture-beta\n    group api(cloud)[API]\n    service db \"\u003cimg src=x onerror=\\\"alert(document.domain)\\\"\u003e\" [Database] in api\n```\n2. The XSS should pop whenever either repository or file is viewed\n\n#### Demo\n\nhttps://github.com/user-attachments/assets/98320f62-6c1c-4254-aa61-95598c725235\n\n### Impact\nThe attacker can potentially achieve account takeover\nIn a worst case scenario if the victim were an instance admin this could lead to a compromise of the entire deployment\n\n### Proposed remediation steps\n1. Upgrade to a patched version of the third party library\nhttps://github.com/mermaid-js/mermaid/releases/tag/v10.9.5\n2. Consider running mermaid using `sandbox` level which would mitigate impact of future potential cross-site scripting issues\nhttps://mermaid.js.org/config/usage.html#securitylevel","status":"published","published":"2026-02-06T19:44:14Z","modified":"2026-02-06T19:44:14Z","cvss":[{"version":"3.1","score":7.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N","level":"high"}],"cwes":["CWE-79","CWE-1395"],"updated_at":"2026-11-02T14:39:23.728882Z"}],"osv":[{"id":"GHSA-26gq-grmh-6xm6","title":"Gogs vulnerable to Stored XSS via Mermaid diagrams","description":"### Summary\nStored XSS via mermaid diagrams due to usage of vulnerable renderer library\n\n### Details\nGogs introduced support for rendering mermaid diagrams in version [0.13.0.](https://github.com/gogs/gogs/releases/tag/v0.13.0)\n\nCurrently used version of the library [mermaid 11.9.0](https://github.com/gogs/gogs/tree/main/public/plugins/mermaid-11.9.0) is vulnerable to at least two XSS scenarios with publicly available payloads\n\nResources:\nhttps://github.com/mermaid-js/mermaid/security/advisories/GHSA-7rqq-prvp-x9jh\nhttps://github.com/mermaid-js/mermaid/security/advisories/GHSA-8gwm-58g9-j8pw\n\n### PoC\n\n1. Create a markdown file eg. `README.md` containing following malicious mermaid diagram (payload based on [CVE-2025-54880](https://github.com/mermaid-js/mermaid/security/advisories/GHSA-8gwm-58g9-j8pw))\n```\narchitecture-beta\n    group api(cloud)[API]\n    service db \"\u003cimg src=x onerror=\\\"alert(document.domain)\\\"\u003e\" [Database] in api\n```\n2. The XSS should pop whenever either repository or file is viewed\n\n#### Demo\n\nhttps://github.com/user-attachments/assets/98320f62-6c1c-4254-aa61-95598c725235\n\n### Impact\nThe attacker can potentially achieve account takeover\nIn a worst case scenario if the victim were an instance admin this could lead to a compromise of the entire deployment\n\n### Proposed remediation steps\n1. Upgrade to a patched version of the third party library\nhttps://github.com/mermaid-js/mermaid/releases/tag/v10.9.5\n2. Consider running mermaid using `sandbox` level which would mitigate impact of future potential cross-site scripting issues\nhttps://mermaid.js.org/config/usage.html#securitylevel","status":"published","published":"2026-02-06T19:44:14Z","modified":"2026-02-19T20:41:26.142855Z","cvss":[{"version":"3.1","score":7.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N","level":"high"}],"cwes":["CWE-1395","CWE-79"],"updated_at":"2026-11-02T15:46:33.956911Z"},{"id":"GO-2026-4454","title":"Gogs vulnerable to Stored XSS via Mermaid diagrams in gogs.io/gogs","description":"Gogs vulnerable to Stored XSS via Mermaid diagrams in gogs.io/gogs.\n\nNOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions.\n\n(If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.)\n\nThe additional affected modules and versions are: gogs.io/gogs before v0.13.4.","status":"published","published":"2026-02-17T18:09:06Z","modified":"2026-02-19T20:41:26.142855Z","updated_at":"2026-11-02T15:47:02.011123Z"}]}}