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Description

A server-side request forgery (SSRF) vulnerability was identified in the GitHub Enterprise Server notebook viewer that allowed an attacker to access internal services by exploiting URL parser confusion between the validation layer and the HTTP request library. The hostname validation used a different URL parser than the request library, enabling a crafted URL to pass validation while directing the request to an unintended host. Exploitation required network access to the GitHub Enterprise Server instance. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.16.18, 3.17.15, 3.18.9, 3.19.6, and 3.20.2. This vulnerability was reported via the GitHub Bug Bounty program.

PUBLISHED Reserved 2026-05-06 | Published 2026-05-07 | Updated 2026-05-08 | Assigner GitHub_P




HIGH: 7.9CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H

Problem types

CWE-918 Server-Side request forgery (SSRF)

CWE-436 Interpretation Conflict

Product status

Default status
affected

3.16.0 (semver)
affected

3.17.0 (semver)
affected

3.18.0 (semver)
affected

3.19.0 (semver)
affected

3.20.0 (semver)
affected

3.21.0 (semver)
unaffected

Credits

R31n finder

References

docs.github.com/...nterprise-server@3.16/admin/release-notes release-notes

docs.github.com/...nterprise-server@3.17/admin/release-notes release-notes

docs.github.com/...nterprise-server@3.18/admin/release-notes release-notes

docs.github.com/...nterprise-server@3.19/admin/release-notes release-notes

docs.github.com/...nterprise-server@3.20/admin/release-notes release-notes

cve.org (CVE-2026-8034)

nvd.nist.gov (CVE-2026-8034)

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