CVE-2026-77912
mediumpriority · track · 22EPSS 0.002 · 11 %ileDEUSEPSS · scored 2026-10-27
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
Technical severity, 0–10. One row per scoring source.
base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 4.5–7.4
ssvc
A stakeholder decision — act, attend, or track — from exploitation and impact.
weaknesses
The CWE weakness classes this flaw belongs to.
affected products (18)
Products and version ranges known to be affected.
advisories (1)
Vendor and ecosystem advisories describing this.
- WID-SEC-W-2026-3530Microsoft GitHub Enterprise Server: Mehrere SchwachstellenDeutsch2026-09-22csaf · cert_bundDE
Ein Angreifer kann mehrere Schwachstellen in Microsoft GitHub Enterprise Server ausnutzen, um Informationen offenzulegen, Daten zu manipulieren, beliebigen Code auszuführen oder Cross-Site-Scripting-Angriffe durchzuführen.
sources
Which sources assert this record, and when.
references (6) nvd
External citations — patches, advisories, analysis.
- https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.21Release NotesVendor Advisory
- https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.15Release NotesVendor Advisory
- https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.12Release NotesVendor Advisory
- https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.8Release NotesVendor Advisory
- https://docs.github.com/en/enterprise-server@3.21/admin/release-notes#3.21.6Release NotesVendor Advisory
- https://docs.github.com/en/enterprise-server@3.22/admin/release-notes#3.22.1Release NotesVendor Advisory
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