A stored XSS flaw in GitHub Enterprise Server permits an authenticated attacker to inject arbitrary HTML attributes through Markdown rendering. The pipeline rewrites quote characters in already‑sanitized HTML without re‑sanitizing, allowing same‑origin JavaScript gadgets to bypass the Content Security Policy. When a victim views the rendered content, the attacker can read visible data, capture CSRF tokens, perform state‑changing actions on the victim’s behalf, and exfiltrate data via same‑origin mechanisms. The payload may propagate to any repositories or organizations where the victim has write access.

GitHub Enterprise Server releases in the 3.17, 3.18, 3.19, 3.20, 3.21, and 3.22 series are affected. The issue is fixed in the following releases: 3.22.1, 3.21.6, 3.20.8, 3.19.12, 3.18.15, and 3.17.21.

The vulnerability scores a CVSS of 7.4, with no EPSS data available and it is not listed in the CISA KEV catalog. Exploitation requires authentication and write access to a repository or organizational content to inject malicious Markdown. Once injected, the payload is executed when viewed by another authenticated user, enabling extensive DOM manipulation and potential data exfiltration.