CVE-2026-77912: Stored cross-site scripting vulnerability in GitHub Enterprise Server allowed HTML attribute injection via the Markdown rendering pipeline
Noroxi assessment
Priority: Monitor (action score 29/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 0.20% (FIRST EPSS).
- Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. Special conditions such as timing or configuration are required.
- Fixed version: GitHub Enterprise Server 3.17.*, 3.17.21, 3.18.*.
Low priority for now. Upgrade to GitHub Enterprise Server 3.17.*, 3.17.21, 3.18.* or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
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.
- Published
- Sep 22, 2026
- Updated
- Oct 2, 2026
- EPSS
- 0.2% · 10th percentile
- CWE
- CWE-79
Report tools
Action score
29
Monitor
Low priority for now.
- CVSS
- 29 / 40 · 7.4 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.2%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- total
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · GitHub_P
- 7.4
- NVD has not scored this yet; the score shown is the CNA’s.
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
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| github | enterprise server | cpe:2.3:a:github:enterprise_server |
Limit the impact of XSS
This is a cross-site scripting (XSS) vulnerability. A well-configured Content-Security-Policy doesn't fix it, but greatly reduces its impact. Check your site's CSP and other security headers for free.
Check security headersAffected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- github enterprise server3.17.0 and later · before 3.17.21
- github enterprise server3.18.0 and later · before 3.18.15
- github enterprise server3.19.0 and later · before 3.19.12
- github enterprise server3.20.0 and later · before 3.20.8
- github enterprise server3.21.0 and later · before 3.21.6
- github enterprise server3.22.0 and later · before 3.22.1
Versions reported by the vendor
Affected version ranges reported by the assigning authority (GitHub_P). Independent of NVD's CPE analysis and usually ahead of it.
GitHub Enterprise Server
- 3.17.0 and later · before 3.17.*affected · semverfixed in 3.17.21
- 3.18.0 and later · before 3.18.*affected · semverfixed in 3.18.15
- 3.19.0 and later · before 3.19.*affected · semverfixed in 3.19.12
- 3.20.0 and later · before 3.20.*affected · semverfixed in 3.20.8
- 3.21.0 and later · before 3.21.*affected · semverfixed in 3.21.6
- 3.22.0 and later · before 3.22.*affected · semverfixed in 3.22.1
Same product
github: all recordsOther highest-scoring records for the same primary product.
- CVE-2024-0200Unsafe Reflection in Github Enterprise Server leading to Command Injection61This week
- CVE-2024-0507Privilege Escalation by Code Injection in the Management Console in GitHub Enterprise Server55Plan
- CVE-2026-3854Remote code execution via git push option injection in GitHub Enterprise Server46Plan
Published before and after this one in the same product
- ← EarlierCVE-2026-76851Sep 1, 2026 · Server-Side Request Forgery vulnerability in GitHub Enterprise Server allowed remote code execution via network access from pre-receive hooks to internal servic30Monitor
- ← EarlierCVE-2026-75101Sep 22, 2026 · Authorization bypass vulnerability in GitHub Enterprise Server allowed reading of private pull request diffs and patches via repository name collision24Monitor
- Later →CVE-2026-77987Sep 22, 2026 · GitHub Enterprise Server notebook viewer vulnerable to Server-side request forgery37Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| GitHub Enterprise Server | 3.17.* | Vendor (CNA) |
| GitHub Enterprise Server | 3.17.21 | Vendor (CNA) |
| GitHub Enterprise Server | 3.18.* | Vendor (CNA) |
| GitHub Enterprise Server | 3.18.15 | Vendor (CNA) |
| GitHub Enterprise Server | 3.19.* | Vendor (CNA) |
| GitHub Enterprise Server | 3.19.12 | Vendor (CNA) |
| GitHub Enterprise Server | 3.20.* | Vendor (CNA) |
| GitHub Enterprise Server | 3.20.8 | Vendor (CNA) |
| GitHub Enterprise Server | 3.21.* | Vendor (CNA) |
| GitHub Enterprise Server | 3.21.6 | Vendor (CNA) |
| GitHub Enterprise Server | 3.22.* | Vendor (CNA) |
| GitHub Enterprise Server | 3.22.1 | Vendor (CNA) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
- ahacker1finder
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
- CVE-2025-14046285 days apartInsufficient HTML Sanitization Allows User-Controlled DOM Elements to Overwrite Server-Initialized Data Islands and Trigger Unintended Server-Side POST Requests34Monitor
- CVE-2025-11892316 days apartDOM-based Cross-Site Scripting was identified in GitHub Enterprise Server Issues search allows privilege escalation and unauthorized workflow triggers34Monitor
- CVE-2025-3246523 days apartMarkdown math block sanitization bypass allows privilege escalation and unauthorized workflow triggers34Monitor
- CVE-2025-13744259 days apartImproper Neutralization of Input During Web Page Generation vulnerability was identified in GitHub Enterprise Server that allowed rendering of malicious HTML33Monitor
- CVE-2026-2266196 days apartImproper neutralization of input vulnerability was identified in GitHub Enterprise Server that allowed cross-site scripting via task list content and enabled ar29Monitor
- CVE-2026-1058584 days apartStored cross-site scripting vulnerability in GitHub Enterprise Server allowed arbitrary JavaScript execution via crafted Discussion titles in the Q&A category25Monitor
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- A low-privileged account is enough.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- Integrity
- Availability
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- Low
- User interaction
- P
- Scope
- X
Weakness class (CWE)
CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')CVSS vector
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-secondary
Root cause
User content is inserted into the page as HTML. The browser interprets the content as code rather than data.
The bug in code
The whole CWE-79 classA representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.
Vulnerable
commentEl.innerHTML = comment.body;Fixed
commentEl.textContent = comment.body;Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
ATT&CK techniques
—
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (5 more)Show less
- docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.15
- docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.12
- docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.8
- docs.github.com/en/enterprise-server@3.21/admin/release-notes#3.21.6
- docs.github.com/en/enterprise-server@3.22/admin/release-notes#3.22.1
Vendor advisories and official records. Exploit/PoC links are deliberately left out.