Server-Side Request Forgery in GitHub Enterprise Server allowed extraction of sensitive environment variables via timing side-channel attack

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Summary

CVECVE-2026-5921
StatePUBLISHED
AssignerGitHub_P
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-21 23:16:22 UTC
Updated2026-04-22 21:23:52 UTC
DescriptionA 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.

Risk And Classification

Primary CVSS: v4.0 8.9 HIGH from [email protected]

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/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS: 0.000490000 probability, percentile 0.151090000 (date 2026-04-22)

Problem Types: CWE-918 | CWE-918 CWE-918 Server-Side Request Forgery (SSRF)

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary8.9HIGHCVSS: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/C...
4.0CNACVSS8.9HIGHCVSS: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

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
High
Attack Requirements
Present
Privileges Required
None
User Interaction
None
Confidentiality
High
Integrity
High
Availability
Low
Sub Conf.
High
Sub Integrity
High
Sub Availability
Low

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/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA GitHub Enterprise Server affected 3.14.0 3.14.26 semver Not specified
CNA GitHub Enterprise Server affected 3.15.0 3.15.21 semver Not specified
CNA GitHub Enterprise Server affected 3.16.0 3.16.17 semver Not specified
CNA GitHub Enterprise Server affected 3.17.0 3.17.14 semver Not specified
CNA GitHub Enterprise Server affected 3.18.0 3.18.8 semver Not specified
CNA GitHub Enterprise Server affected 3.19.0 3.19.5 semver Not specified
CNA GitHub Enterprise Server affected 3.20.0 3.20.1 semver Not specified

References

ReferenceSourceLinkTags
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com
docs.github.com/en/[email protected]/admin/release-notes [email protected] docs.github.com
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Vendor Comments And Credit

Discovery Credit

CNA: R31n (en)

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