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

> CVE-2026-77987: GitHub Enterprise Server notebook viewer vulnerable to Server-side request forgery. CVSS 9.8 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-77987
Last updated: 2026-10-02T18:37:45Z

- Published: 2026-09-22 20:43 UTC · Updated: 2026-10-02 18:37 UTC · Assigner: GitHub\_P
- CVSS: 9.8 (CVSS 3.1) · Severity: Critical · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS: 0.88%, 59th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-208, CWE-918

## 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.

## Affected vendors and products

- GitHub: Enterprise Server

## Tracked companies

- [GitHub](https://rewindex.com/company/github.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-77987)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-77987)
- [https://docs.github.com/en/enterprise-server@3.17/admin/release-notes\#3.17.21](https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.21)
- [https://docs.github.com/en/enterprise-server@3.18/admin/release-notes\#3.18.15](https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.15)
- [https://docs.github.com/en/enterprise-server@3.19/admin/release-notes\#3.19.12](https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.12)
- [https://docs.github.com/en/enterprise-server@3.20/admin/release-notes\#3.20.8](https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.8)
- [https://docs.github.com/en/enterprise-server@3.21/admin/release-notes\#3.21.6](https://docs.github.com/en/enterprise-server@3.21/admin/release-notes#3.21.6)
- [https://docs.github.com/en/enterprise-server@3.22/admin/release-notes\#3.22.1](https://docs.github.com/en/enterprise-server@3.22/admin/release-notes#3.22.1)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-77987 · Markdown: https://rewindex.com/cve/CVE-2026-77987.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-77987 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T02:49:47.987Z