# CVE-2026-77987: GitHub Enterprise Server notebook viewer SSRF

Source: https://junglewise.ai/threats/cve-2026-77987-a-server-side-request-forgery-ssrf-vulnerability-was-identified  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-22. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-77987 · Severity: info · Published 2026-09-22

GitHub Enterprise Server contains a server-side request forgery (SSRF) vulnerability in its notebook viewer component that allows an attacker to send requests to internal services on the appliance. By exploiting timing side-channels, an attacker can extract instance secrets character-by-character, then use those secrets to gain remote code execution on the appliance. The vulnerability affects unpatched instances and requires network access, with minimal or no authentication required depending on the instance's private mode setting.

Technologies: [GitHub Enterprise Server](https://junglewise.ai/threats/technologies/github-enterprise-server). Vendors: [GitHub](https://junglewise.ai/threats/vendors/github).

## Quick answers

**Is CVE-2026-77987 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-77987 being exploited in the wild.

**How severe is CVE-2026-77987?** Informational severity, published 22 September 2026.

**Which products and versions are affected?** GitHub Enterprise Server 3.17 through 3.22 (fixed in 3.17.21, 3.18.15, 3.19.12, 3.20.8, 3.21.6, 3.22.1).

**Is there a fix for CVE-2026-77987?** A patch was published on 2026-09-22: Patches released for versions 3.17.21, 3.18.15, 3.19.12, 3.20.8, 3.21.6, 3.22.1 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-77987 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-77987?** Check whether you run GitHub Enterprise Server at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The notebook viewer validates URL scheme and host but fails to validate the port parameter, allowing an attacker to redirect requests to internal services on alternate ports. Response timing acts as an oracle to extract secrets without returning response bodies. Exploitation chains this information disclosure to perform authenticated requests to internal services, achieving remote code execution. The vulnerability is unauthenticated on instances without private mode enabled, or requires any authenticated user when private mode is enabled.

## Affected products

- GitHub Enterprise Server 3.17 through 3.22 (fixed in 3.17.21, 3.18.15, 3.19.12, 3.20.8, 3.21.6, 3.22.1)

## Timeline

- 2026-09-22: disclosed
- 2026-09-22: patched: Patches released for versions 3.17.21, 3.18.15, 3.19.12, 3.20.8, 3.21.6, 3.22.1

## References

- [https://docs.github.com/en/enterprise-server@3.17/admin/release-notes](https://docs.github.com/en/enterprise-server@3.17/admin/release-notes)
- [https://docs.github.com/en/enterprise-server@3.18/admin/release-notes](https://docs.github.com/en/enterprise-server@3.18/admin/release-notes)

## Related threats

- [GitHub Enterprise Server out-of-bounds read in SSH key negotiation](https://junglewise.ai/threats/cve-2026-118237-an-out-of-bounds-read-vulnerability-was-identified-in-github)
- [GitHub Enterprise Server CSRF in ChatOps integration removal](https://junglewise.ai/threats/cve-2026-110288-a-cross-site-request-forgery-vulnerability-was-identified-in)
- [GitHub Enterprise Server use-after-free in Git service babeld](https://junglewise.ai/threats/cve-2026-104608-a-remote-code-execution-vulnerability-was-identified-in-github)
- [GitHub Enterprise Server SSRF in secret scanning validator](https://junglewise.ai/threats/cve-2026-96890-a-server-side-request-forgery-ssrf-vulnerability-was-identified)
- [GitHub Enterprise Server missing authorization in GraphQL API](https://junglewise.ai/threats/cve-2026-103620-a-missing-authorization-vulnerability-was-identified-in-github)