CVE-2026-77912

Vulnerability 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.

CVSS Score

Affected Products

Related Weaknesses (CWE)

References

• https://docs.github.com/en/[email protected]/admin/release-notes#3.17.21Release NotesVendor Advisory
• https://docs.github.com/en/[email protected]/admin/release-notes#3.18.15Release NotesVendor Advisory
• https://docs.github.com/en/[email protected]/admin/release-notes#3.19.12Release NotesVendor Advisory
• https://docs.github.com/en/[email protected]/admin/release-notes#3.20.8Release NotesVendor Advisory
• https://docs.github.com/en/[email protected]/admin/release-notes#3.21.6Release NotesVendor Advisory
• https://docs.github.com/en/[email protected]/admin/release-notes#3.22.1Release NotesVendor Advisory