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CVE-2026-77987

9.8, critical

A server-side request forgery (SSRF) vulnerability was identified in the notebook viewer of GitHub Enterprise Server

NVD (opens in a new tab) CVE.org (opens in a new tab)
CVSS
9.8, critical critical CVSS v3.1
EPSS, next 30 days
0.9% higher than 58.2% of scored CVEs
Exploitation
No public evidence
Published
22 Sept 202625 days ago

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.

Details

Vendor
GitHub
Product
Enterprise Server
Weakness
CWE-208 (opens in a new tab)
Status
Analyzed
Updated
2 Oct 2026
Assigner
product-cna@github.com

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References 6

Advisories 6

The kind is read from NVD's tags where present and from the shape of the URL otherwise, so treat it as a hint.

Other GitHub CVEs

Every GitHub CVE we hold

Same vendor in what we hold, not a known link between the flaws.

  • CVE-2026-96890 GitHub Enterprise Server Server-Side Request Forgery Vulnerability EPSS 0.5% 8.8, high
  • CVE-2026-18730 GitHub Enterprise Server Server-Side Request Forgery Vulnerability EPSS 0.3% 7.4, high
  • CVE-2026-19118 GitHub Enterprise Server Time-of-Check Time-of-Use Race Condition Vulnerability EPSS 0.7% 7.5, high
  • CVE-2026-76851 GitHub Enterprise Server Server-Side Request Forgery Vulnerability EPSS 0.8% 8.8, high

Beyond this page

Is CVE-2026-77987 in your network?

This page tells you how dangerous CVE-2026-77987 is out there. Whether it sits on one of your devices, only a scan of your own network can tell. That is what our systems do, every day, for the companies we protect.

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Check your exposure

Assembled from the NVD 2.0 API, the CISA Known Exploited Vulnerabilities Catalog and FIRST EPSS. Scores are as of our last collection on 17 Oct 2026, not the live upstream state.