CVE-2026-77912 json
Stored cross-site scripting vulnerability in GitHub Enterprise Server allowed HTML attribute injection via the Markdown rendering pipeline
published 2026-09-22 47 d ago modified 2026-10-02 37 d ago also EUVD-2026-84873
- cvss
- 5.4
- version 3.1, NVD
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.2%
- EPSS 0.2% chance of exploitation in 30 days, percentile 10%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- GitHub Enterprise Server 3.17.21, 3.18.15, 3.19.12, 3.20.8, 3.21.6, 3.22.1
CISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- total
- Assessed
- 46 d ago
Exploit prediction
0.21% chance of exploitation in the next 30 days, higher than 10% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 4.0 | 7.4 | 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 |
| CNA | 4.0 | 7.4 | 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:Y/R:X/V:X/RE:X/U:X |
| NVD | 3.1 | 5.4 | CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N |
Affected products
- GitHub Enterprise Server
Classification
- Weakness
-
- CWE-79 Improper Neutralization of Input During Web Page Generation
References
-
docs.github.com
/en/enterprise-server@3.17/admin/release-notes#3.17.21
release-notes, vendor-advisory
-
docs.github.com
/en/enterprise-server@3.18/admin/release-notes#3.18.15
release-notes, vendor-advisory
-
docs.github.com
/en/enterprise-server@3.19/admin/release-notes#3.19.12
release-notes, vendor-advisory
-
docs.github.com
/en/enterprise-server@3.20/admin/release-notes#3.20.8
release-notes, vendor-advisory
-
docs.github.com
/en/enterprise-server@3.21/admin/release-notes#3.21.6
release-notes, vendor-advisory
-
docs.github.com
/en/enterprise-server@3.22/admin/release-notes#3.22.1
release-notes, vendor-advisory
Sources
- CVE List CVE-2026-77912
- NVD CVE-2026-77912
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