GitHub Enterprise Server XSS via Markdown sanitization (3.17-3.22)
CVE-2026-77912 Published on September 22, 2026

Stored cross-site scripting vulnerability in GitHub Enterprise Server allowed HTML attribute injection via the Markdown rendering pipeline
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.

NVD

Vulnerability Analysis

CVE-2026-77912 is exploitable with network access. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity and availability.

Attack Vector:
NETWORK
Attack Complexity:
HIGH
Privileges Required:
LOW
User Interaction:
PASSIVE

Weakness Type

What is a XSS Vulnerability?

The software does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

CVE-2026-77912 has been classified to as a XSS vulnerability or weakness.


Products Associated with CVE-2026-77912

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github Enterprise Server
 

Affected Versions

GitHub Enterprise Server: