GitHub Enterprise Server notebook viewer vulnerable to Server-side request forgery

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-77987
StatePUBLISHED
AssignerGitHub_P
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-22 21:17:32 UTC
Updated2026-09-24 21:16:28 UTC
DescriptionA server-side request forgery (SSRF) vulnerability was identified in the notebook viewer of GitHub Enterprise Server. The notebook viewer validated the scheme and host of a user-supplied URL but did not validate the port, allowing requests to be directed to internal services listening on other ports of the same appliance. Response bodies were not returned to the requester, but response timing acted as an oracle that allowed instance secrets to be extracted character by character. An extracted secret could then be used in a separate interaction with an internal service to obtain remote code execution on the appliance. Exploitation required network access to the instance and was unauthenticated when private mode was disabled, or required any authenticated user when private mode was enabled. This vulnerability affected GitHub Enterprise Server versions 3.17 through 3.22 and was fixed in versions 3.22.1, 3.21.6, 3.20.8, 3.19.12, 3.18.15, and 3.17.21. This vulnerability was reported through the GitHub Bug Bounty program.

Risk And Classification

Primary CVSS: v4.0 9.3 CRITICAL from [email protected]

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/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: 0.008910000 probability, percentile 0.576320000 (date 2026-09-24)

Problem Types: CWE-208 | CWE-918 | CWE-918 CWE-918 Server-Side Request Forgery (SSRF) | CWE-208 CWE-208 Observable Timing Discrepancy

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary9.3CRITICALCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/C...
4.0CNACVSS9.3CRITICALCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

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

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/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 3.17.0 3.17.* semver Not specified
CNA GitHub Enterprise Server affected 3.18.0 3.18.* semver Not specified
CNA GitHub Enterprise Server affected 3.19.0 3.19.* semver Not specified
CNA GitHub Enterprise Server affected 3.20.0 3.20.* semver Not specified
CNA GitHub Enterprise Server affected 3.21.0 3.21.* semver Not specified
CNA GitHub Enterprise Server affected 3.22.0 3.22.* 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
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Seokchan Yoon (en)

CNA: R31n (en)

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