FXeSECVulnerability intelligence
CVE / 2026 / 77987

GitHub Enterprise Server notebook viewer vulnerable to SSRF

A server-side request forgery vulnerability in the notebook viewer could allow requests to internal services on other ports of the same appliance.

CVSS v4.0 9.3 · CRITICAL

CVE description

The notebook viewer validated the scheme and host of a user-supplied URL but did not validate the port. This allowed requests to be directed to internal services listening on other ports of the appliance.

Response bodies were not returned, 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. It was unauthenticated when private mode was disabled, or required any authenticated user when private mode was enabled.

CVSS metrics

Version4.0
Score9.3 — Critical
VectorCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Attack vectorNetwork
Attack complexityLow
Attack requirementsNone
Privileges requiredNone when private mode is disabled; any authenticated user when private mode is enabled.
User interactionNone
ImpactHigh confidentiality, integrity, and availability impact.

Related weaknesses and remediation

CWE-918 — Server-Side Request Forgery. The server retrieves a user-supplied URL without sufficiently ensuring that the request reaches the expected destination.

CWE-208 — Observable Timing Discrepancy. Differences in operation timing can reveal security-relevant information.

Affected versions: 3.17 through 3.22. Fixed in 3.22.1, 3.21.6, 3.20.8, 3.19.12, 3.18.15, and 3.17.21. FXeSEC recommends applying the fixed release.