CVE-2026-5921— Server-Side Request Forgery in GitHub Enterprise Server allowed extraction of sensitive environment variables via timing side-channel attack
Quick assessment
Affected
GitHub Enterprise Server
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
GitHub Enterprise Server是美国GitHub开源的一个应用软件。提供一个将自己的GitHub实例设置为虚拟设备，从而提供可扩展，易于管理的平台。 GitHub Enterprise Server 3.21之前版本存在安全漏洞，该漏洞源于笔记本渲染服务存在服务端请求伪造，可能导致攻击者通过定时侧信道攻击提取敏感环境变量。
Possible ATT&CK Techniques 3 AI
T1059 · Command and Scripting Interpreter T1190 · Exploit Public-Facing Application T1598 · Phishing for Information
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I. Basic Information for CVE-2026-5921
Vulnerability Information
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Vulnerability Title
Server-Side Request Forgery in GitHub Enterprise Server allowed extraction of sensitive environment variables via timing side-channel attack
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L/E:P
Source: CVE Program / CVE List V5
Vulnerability Type
服务端请求伪造(SSRF)
Source: CVE Program / CVE List V5
Vulnerability Title
GitHub Enterprise Server 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
GitHub Enterprise Server是美国GitHub开源的一个应用软件。提供一个将自己的GitHub实例设置为虚拟设备，从而提供可扩展，易于管理的平台。 GitHub Enterprise Server 3.21之前版本存在安全漏洞，该漏洞源于笔记本渲染服务存在服务端请求伪造，可能导致攻击者通过定时侧信道攻击提取敏感环境变量。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| GitHub | Enterprise Server | 3.14.0 ~ 3.14.26 | - |
|
II. Public POCs for CVE-2026-5921
| # | POC Description | Source Link | Shenlong Link |
|---|
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Vendor Pages for CVE-2026-5921 (1)
Same Patch Batch · GitHub · 2026-04-21 · 5 CVEs total
| CVE-2026-3307 | Authorization bypass in GitHub Enterprise Server secret scanning push protection allows cr | |
| CVE-2026-4296 | Incorrect Regular Expression vulnerability in GitHub Enterprise Server allowed unauthorize | |
| CVE-2026-5512 | Improper authorization vulnerability in GitHub Enterprise Server allowed disclosure of pri | |
| CVE-2026-5845 | Improper authorization fallback allows scoped user-to-server token installation escape in |
IV. Related Vulnerabilities
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Same vendor: GitHub
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Same weakness: CWE-918
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Server-side request forgery in the OAuth2 discovery handling
V. Comments for CVE-2026-5921
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