# CVE-2026-5921: A server-side request forgery (SSRF) vulnerability was identified in GitHub Enterprise Server that allowed an attacker…

Source: https://junglewise.ai/threats/cve-2026-5921-a-server-side-request-forgery-ssrf-vulnerability-was-identified-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-21  
License: CC BY 4.0 with a link back

CVE-2026-5921 · Severity: high · CVSS 8.9 · Published 2026-04-21

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.

Technologies: [GitHub Enterprise Server](https://junglewise.ai/threats/technologies/github-enterprise-server). Vendors: [GitHub](https://junglewise.ai/threats/vendors/github).

## Quick answers

**Is CVE-2026-5921 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-5921 being exploited in the wild.

**How severe is CVE-2026-5921?** High severity, with a CVSS score of 8.9, published 21 April 2026.

**Which products and versions are affected?** GitHub Enterprise Server. The advisory does not name versions.

**Is there a fix for CVE-2026-5921?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**Am I affected by CVE-2026-5921?** Check whether you run GitHub Enterprise Server. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Affected products

- GitHub Enterprise Server

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