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CVE-2026-77912— Stored cross-site scripting vulnerability in GitHub Enterprise Server allowed HTML attribute injection via the Markdown rendering pipeline

Quick assessment

Affected
GitHub Enterprise Server
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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 a

CVSS 7.4 · High
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I. Basic Information for CVE-2026-77912

Vulnerability Information

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Vulnerability Title
Stored cross-site scripting vulnerability in GitHub Enterprise Server allowed HTML attribute injection via the Markdown rendering pipeline
Source: CVE Program / CVE List V5
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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
GitHub Enterprise Server 3.17.0 ~ 3.17.* -

II. Public POCs for CVE-2026-77912

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III. Intelligence Information for CVE-2026-77912

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Other References for CVE-2026-77912 (6)

Same Patch Batch · GitHub · 2026-09-22 · 3 CVEs total

CVE-2026-77987 9.3 CRITICAL GitHub Enterprise Server notebook viewer vulnerable to Server-side request forgery
CVE-2026-75101 6.0 MEDIUM Authorization bypass vulnerability in GitHub Enterprise Server allowed reading of private

IV. Related Vulnerabilities

Same product: Enterprise Server
Same vendor: GitHub
Same weakness: CWE-79

V. Comments for CVE-2026-77912

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