# CVE-2026-5921: Server-Side Request Forgery in GitHub Enterprise Server allowed extraction of sensitive environment variables via timing side-channel attack

> CVE-2026-5921: Server-Side Request Forgery in GitHub Enterprise Server allowed extraction of sensitive environment variables via timing side-channel attack. CVSS 8.9 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-5921
Last updated: 2026-06-17T10:59:54Z

- Published: 2026-04-21 22:11 UTC · Updated: 2026-06-17 10:59 UTC · Assigner: GitHub\_P
- CVSS: 8.9 (CVSS 3.1) · Severity: High · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L
- EPSS: 0.42%, 36th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-918

## 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.

## Affected vendors and products

- GitHub: Enterprise Server

## Tracked companies

- [GitHub](https://rewindex.com/company/github.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-5921)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-5921)
- [https://docs.github.com/en/enterprise-server@3.14/admin/release-notes\#3.14.26](https://docs.github.com/en/enterprise-server@3.14/admin/release-notes#3.14.26)
- [https://docs.github.com/en/enterprise-server@3.15/admin/release-notes\#3.15.21](https://docs.github.com/en/enterprise-server@3.15/admin/release-notes#3.15.21)
- [https://docs.github.com/en/enterprise-server@3.16/admin/release-notes\#3.16.17](https://docs.github.com/en/enterprise-server@3.16/admin/release-notes#3.16.17)
- [https://docs.github.com/en/enterprise-server@3.17/admin/release-notes\#3.17.14](https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.14)
- [https://docs.github.com/en/enterprise-server@3.18/admin/release-notes\#3.18.8](https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.8)
- [https://docs.github.com/en/enterprise-server@3.19/admin/release-notes\#3.19.5](https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.5)
- [https://docs.github.com/en/enterprise-server@3.20/admin/release-notes\#3.20.1](https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.1)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-5921 · Markdown: https://rewindex.com/cve/CVE-2026-5921.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-5921 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T02:17:08.525Z