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Description

An authentication bypass vulnerability was identified in GitHub Enterprise Server that allowed an unauthenticated attacker to create a local user account, bypassing the configured external identity provider. When external authentication was enabled, the signup endpoint did not properly enforce the authentication restriction, allowing account creation and session establishment without identity provider validation. The created account was limited to the default base permissions configured on the instance. Exploitation required network access to a GHES instance configured with an external authentication provider. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.20.2, 3.19.6, 3.18.9, 3.17.15, and 3.16.18.

PUBLISHED Reserved 2026-04-21 | Published 2026-05-07 | Updated 2026-05-08 | Assigner GitHub_P




MEDIUM: 6.3CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Problem types

CWE-306 Missing Authentication for Critical Function

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

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-2026-6736)

nvd.nist.gov (CVE-2026-6736)

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