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.
CVE-2026-77912
This high-severity CVE scores 7.4 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4%, top 61% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
- High severity, but no confirmed exploitation yet
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 7.4
- EG Score
- 7.4(medium)
- EG Risk
- 33(Track)EG Risk 33/100SSVC: Track
EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).
How it’s computedSeverity74% × 45%Exploitation0% × 40%Automatability0% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
- 0%
- EPSS %ILE
- 39%
- KEV
- Not listed
Published
September 22, 2026
Last Modified
September 23, 2026
Advisory Details (6)
Auto-updated Sep 22, 2026Release notes - GitHub Enterprise Server 3.22 Docs
https://docs.github.com/en/[email protected]/admin/release-notes#3.22.1Release notes - GitHub Enterprise Server 3.21 Docs
https://docs.github.com/en/[email protected]/admin/release-notes#3.21.6Release notes - GitHub Enterprise Server 3.20 Docs
https://docs.github.com/en/[email protected]/admin/release-notes#3.20.8Release notes - GitHub Enterprise Server 3.19 Docs
https://docs.github.com/en/[email protected]/admin/release-notes#3.19.12Release notes - GitHub Enterprise Server 3.18 Docs
https://docs.github.com/en/[email protected]/admin/release-notes#3.18.15Release notes - GitHub Enterprise Server 3.17 Docs
https://docs.github.com/en/[email protected]/admin/release-notes#3.17.21Vendor Advisories for CVE-2026-77912(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 12× in last 7d / 12× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-09-24 03:55 UTCEG score recompute
- 2026-09-24 03:55 UTCGHSA enrichment
- 2026-09-23 17:54 UTCEPSS rescore
- 2026-09-23 15:20 UTCEG score recompute
- 2026-09-23 15:20 UTCGHSA enrichment
- 2026-09-23 15:15 UTCEG score recompute
- 2026-09-23 15:15 UTCGHSA enrichment
- 2026-09-23 10:07 UTCGHSA enrichment
- 2026-09-22 21:33 UTCEG score recompute
- 2026-09-22 21:33 UTCGHSA enrichment
- 2026-09-22 20:48 UTCEG score recompute
- 2026-09-22 20:47 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Frequently asked(5)
What is CVE-2026-77912?
When was CVE-2026-77912 disclosed?
Is CVE-2026-77912 actively exploited?
What is the CVSS score of CVE-2026-77912?
How do I remediate CVE-2026-77912?
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-77912
Is Your Infrastructure Affected by CVE-2026-77912?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.