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

> Attacker can exploit SSRF in notebook viewer to extract secrets and achieve remote code execution on GitHub Enterprise Server.

- **Severity:** Critical 9.3 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 22 Sep 2026
- **Updated:** 23 Sep 2026
- **Also known as:** GHSA-5p5v-w43x-q8v7

## What is CVE-2026-77987?

CVE-2026-77987 is a critical server-side request forgery vulnerability in Github Enterprise Server, published on 22 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-918 (Server-Side Request Forgery), CWE-208 (Observable Timing Discrepancy)

## Which versions are affected by CVE-2026-77987?

It affects 1 product.


Products: Github Enterprise Server.

## How do I fix CVE-2026-77987?

No fix has been published for CVE-2026-77987 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-77987 being exploited?

There is no known exploitation of CVE-2026-77987 in the wild and no public exploit code.

## Other vulnerabilities in Github Enterprise Server

- [CVE-2024-4985](https://insights.sbomify.com/CVE-2024-4985/): Auth bypass in Enterprise Server (critical 10.0)
- [CVE-2022-23739](https://insights.sbomify.com/CVE-2022-23739/): Missing authorization in GitHub Enterprise Server (critical 9.8)
- [CVE-2022-46255](https://insights.sbomify.com/CVE-2022-46255/): Improper Limitation of a Pathname to a Restricted Directory in GitHub Enterprise Server leading to RCE (critical 9.8)
- [CVE-2021-22869](https://insights.sbomify.com/CVE-2021-22869/): Improper access control in GitHub Enterprise Server allows self-hosted runners to execute outside their control group (critical 9.8)
- [CVE-2024-9487](https://insights.sbomify.com/CVE-2024-9487/): Auth bypass in Enterprise Server (critical 9.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77987 and fix it if it is affected.

What it is: CVE-2026-77987 is a critical server-side request forgery vulnerability in Github Enterprise Server, published on 22 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-77987 in the wild and no public exploit code.

Affected product: Github Enterprise Server. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-77987/ (Markdown: https://insights.sbomify.com/CVE-2026-77987/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77987
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77987
- OSV: https://osv.dev/vulnerability/CVE-2026-77987

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-77987/
Summaries are generated and may contain mistakes; the official description above is the record.