CVE-2026-5921
8.9 · HIGHOverview
CVE-2026-5921 is a high-severity vulnerability affecting github enterprise_server. It was published on April 21, 2026 and has a CVSS 3.1 base score of 8.9 (HIGH).
This vulnerability has a CVSS 3.1 base score of 8.9, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
Technical 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
Remediation
Check the references section for vendor advisories and patches from github. Update enterprise_server to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| github | enterprise_server | >= 0, < 3.14.26 | Affected |
References
Frequently Asked Questions
What is CVE-2026-5921?
CVE-2026-5921 is a high-severity vulnerability affecting github enterprise_server. It was published on April 21, 2026 and has a CVSS 3.1 base score of 8.9 (HIGH).
How severe is CVE-2026-5921?
This vulnerability has a CVSS 3.1 base score of 8.9, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2026-5921?
Check the references section for vendor advisories and patches from github. Update enterprise_server to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-5921?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-5921 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
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