Server-side request forgery in GitHub Enterprise Server
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- High
- Attack requirements
- Present
- Impact type
- —
- Confidentiality · integrity · availability
- High · High · Low
- Fix status
- Fixed
Attack profile from CVSS 4.0 · CNA. Fix status from CNA.
Summary
A server-side request forgery (SSRF) vulnerability was identified in GitHub Enterprise Server that allowed an attacker to extract sensitive environment variables from the instance through a timing side-channel attack against the notebook rendering service. When private mode was disabled, the notebook viewer followed HTTP redirects without revalidating the destination host, enabling an unauthenticated SSRF to internal services. By chaining this with regex filter queries against an internal API and measuring response time differences, an attacker could infer secret values character by character. Exploitation required that private mode be disabled and that the attacker be able to chain the instance's open redirect endpoint through an external redirect to reach internal services. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.14.26, 3.15.21, 3.16.17, 3.17.14, 3.18.8, 3.19.5, and 3.20.1. This vulnerability was reported via the GitHub Bug Bounty program.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| GitHub | Enterprise Server | 3.14.0 to before 3.14.26; 3.15.0 to before 3.15.21; 3.16.0 to before 3.16.17; 3.17.0 to before 3.17.14; 3.18.0 to before 3.18.8; 3.19.0 to before 3.19.5; 3.20.0 to before 3.20.1 | 3.14.26, 3.15.21, 3.16.17, 3.17.14, 3.18.8, 3.19.5, 3.20.1 | Patch available | CNA |
- Enterprise Server VendorGitHub Affected 3.14.0 to before 3.14.26; 3.15.0 to before 3.15.21; 3.16.0 to before 3.16.17; 3.17.0 to before 3.17.14; 3.18.0 to before 3.18.8; 3.19.0 to before 3.19.5; 3.20.0 to before 3.20.1 Fixed in 3.14.26, 3.15.21, 3.16.17, 3.17.14, 3.18.8, 3.19.5, 3.20.1 Patch available CNA
CPE configurations NVD · 2
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:github:enterprise_server:*:*:*:*:*:*:*:* | before 3.14.26; 3.15.0 to before 3.15.21; 3.16.0 to before 3.16.17; 3.17.0 to before 3.17.14; 3.18.0 to before 3.18.8; 3.19.0 to before 3.19.5 | Vulnerable | GitHub |
| cpe:2.3:a:github:enterprise_server:3.20.0:*:*:*:*:*:*:* | 3.20.0 | Vulnerable | GitHub |
- cpe:2.3:a:github:enterprise_server:*:*:*:*:*:*:*:* Versions before 3.14.26; 3.15.0 to before 3.15.21; 3.16.0 to before 3.16.17; 3.17.0 to before 3.17.14; 3.18.0 to before 3.18.8; 3.19.0 to before 3.19.5 Vulnerable ·GitHub
- cpe:2.3:a:github:enterprise_server:3.20.0:*:*:*:*:*:*:* Versions 3.20.0 Vulnerable ·GitHub
Remediation
- Fix · CNA Enterprise Server (GitHub) Fixed in 3.14.26, 3.15.21, 3.16.17, 3.17.14, 3.18.8, 3.19.5, 3.20.1
Timeline
- 2026-10-02 Threatist record created from CVE-2026-5921
- 2026-10-03 Alias added: GHSA-2gr8-2hf5-x695
- 2026-10-21 EPSS moved to the 50th–90th percentile
- 2026-10-25 EPSS moved to the below the 50th percentile
References
Advisory 7
- https://docs.github.com/en/[email protected]/admin/release-notes#3.14.26
- https://docs.github.com/en/[email protected]/admin/release-notes#3.15.21
- https://docs.github.com/en/[email protected]/admin/release-notes#3.16.17
- https://docs.github.com/en/[email protected]/admin/release-notes#3.17.14
- https://docs.github.com/en/[email protected]/admin/release-notes#3.18.8
- https://docs.github.com/en/[email protected]/admin/release-notes#3.19.5
- https://docs.github.com/en/[email protected]/admin/release-notes#3.20.1
More GitHub Enterprise Server vulnerabilities
- TI-2024-04632 An authentication bypass vulnerability was present in the GitHub Enterprise Server (GHES)… CVSS 4.0CRITICAL 10.0
- TI-2024-00181 Unsafe Reflection in Github Enterprise Server leading to Command Injection CVSS 3.1CRITICAL 9.8
- TI-2024-00466 Privilege Escalation by Code Injection in the Management Console in GitHub Enterprise Server CVSS 3.1HIGH 8.8
- TI-2026-03340 Remote code execution via git push option injection in GitHub Enterprise Server CVSS 4.0HIGH 8.7
- TI-2024-08804 Improper signature verification in GitHub Enterprise Server CVSS 4.0CRITICAL 9.5
- TI-2026-08177 Server-side request forgery in GitHub Enterprise Server CVSS 4.0CRITICAL 9.2
Sources
- CVE-2026-5921 · CVE Program
- CVE-2026-5921 · NVD
- FIRST EPSS
- GHSA-2gr8-2hf5-x695 · GitHub Advisory Database · CC BY 4.0
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