Vulnerability · Published Sep 22, 2026 · Assigned by GitHub_P
CVE-2026-77912Stored cross-site scripting vulnerability in GitHub Enterprise Server allowed HTML attribute injection via the Markdown rendering pipeline
High 7.4
In plain English
A high-severity cross-site scripting in Enterprise Server from GitHub. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 11% of all known vulnerabilities).
Official description
A stored cross-site scripting (XSS) vulnerability was identified in GitHub Enterprise Server that allowed an authenticated attacker to inject arbitrary HTML attributes into rendered Markdown because the Markdown rendering pipeline rewrote quote characters in already-sanitized HTML without re-sanitizing the result. Crafted Markdown could abuse same-origin JavaScript gadgets to bypass Content Security Policy and gain control of the page DOM when viewed by another user. Successful exploitation could allow an attacker to read content visible to the victim, extract embedded CSRF tokens, perform state-changing actions as the victim, and exfiltrate data through same-origin writes. The payload could also propagate to repositories and organizations where the victim had write access. This vulnerability affected supported GitHub Enterprise Server releases in the 3.17, 3.18, 3.19, 3.20, 3.21, and 3.22 series and was fixed in versions 3.22.1, 3.21.6, 3.20.8, 3.19.12, 3.18.15, and 3.17.21. This vulnerability was reported via the GitHub Bug Bounty program.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| GitHub | Enterprise Server | 3.17.0 – before 3.17.*3.18.0 – before 3.18.*3.19.0 – before 3.19.*3.20.0 – before 3.20.*3.21.0 – before 3.21.*3.22.0 – before 3.22.* |
Weakness: CWE-79 · Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N/AU:Y
References
- https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.21 release-notes
- https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.15 release-notes
- https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.12 release-notes
- https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.8 release-notes
- https://docs.github.com/en/enterprise-server@3.21/admin/release-notes#3.21.6 release-notes
- https://docs.github.com/en/enterprise-server@3.22/admin/release-notes#3.22.1 release-notes