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CVE-2026-77987— GitHub Enterprise Server notebook viewer vulnerable to Server-side request forgery

Quick assessment

Affected
GitHub Enterprise Server
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

A 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 in

CVSS 9.3 · Critical
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I. Basic Information for CVE-2026-77987

Vulnerability Information

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Vulnerability Title
GitHub Enterprise Server notebook viewer vulnerable to Server-side request forgery
Source: CVE Program / CVE List V5
Vulnerability Description
A 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
服务端请求伪造(SSRF)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
GitHub Enterprise Server 3.17.0 ~ 3.17.* -

II. Public POCs for CVE-2026-77987

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III. Intelligence Information for CVE-2026-77987

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Other References for CVE-2026-77987 (6)

Same Patch Batch · GitHub · 2026-09-22 · 3 CVEs total

CVE-2026-77912 7.4 HIGH Stored cross-site scripting vulnerability in GitHub Enterprise Server allowed HTML attribu
CVE-2026-75101 6.0 MEDIUM Authorization bypass vulnerability in GitHub Enterprise Server allowed reading of private

IV. Related Vulnerabilities

Same product: Enterprise Server
Same vendor: GitHub
Same weakness: CWE-918

V. Comments for CVE-2026-77987

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