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.
Published: 2026-04-21
Score: 8.9 High
EPSS: < 1% Very Low
KEV: No
Impact: Sensitive data exposure via SSRF and timing attack
Action: Upgrade
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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories

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History

Tue, 28 Apr 2026 20:45:00 +0000

Type Values Removed Values Added
CPEs cpe:2.3:a:github:enterprise_server:*:*:*:*:*:*:*:*
cpe:2.3:a:github:enterprise_server:3.20.0:*:*:*:*:*:*:*
Metrics cvssV3_1

{'score': 8.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L'}


Wed, 22 Apr 2026 14:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Wed, 22 Apr 2026 04:45:00 +0000

Type Values Removed Values Added
First Time appeared Github
Github enterprise Server
Vendors & Products Github
Github enterprise Server

Wed, 22 Apr 2026 00:00:00 +0000

Type Values Removed Values Added
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.
Title Server-Side Request Forgery in GitHub Enterprise Server allowed extraction of sensitive environment variables via timing side-channel attack
Weaknesses CWE-918
References
Metrics cvssV4_0

{'score': 8.9, 'vector': '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'}


Subscriptions

Github Enterprise Server
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_P

Published:

Updated: 2026-04-22T13:18:03.644Z

Reserved: 2026-04-08T20:59:17.367Z

Link: CVE-2026-5921

cve-icon Vulnrichment

Updated: 2026-04-22T13:17:58.169Z

cve-icon NVD

Status : Analyzed

Published: 2026-04-21T23:16:22.667

Modified: 2026-04-28T20:43:12.443

Link: CVE-2026-5921

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-04-22T06:30:10Z

Weaknesses