# CVE-2026-103620: Missing authorization in GitHub Enterprise Server allowed repository writers to replace default branches via GraphQL

> Repository writers can bypass pull-request review requirements by replacing the default branch via GraphQL, affecting GitHub Enterprise Server.

- **Severity:** Medium 6.0 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 6 Oct 2026
- **Updated:** 7 Oct 2026
- **Also known as:** GHSA-mj9w-xm4p-h2mp

## What is CVE-2026-103620?

CVE-2026-103620 is a medium-severity missing authorization vulnerability in Github Enterprise Server, published on 6 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A missing authorization vulnerability was identified in GitHub Enterprise Server that allowed a repository collaborator with write access to delete the current default branch through the GraphQL API and cause an attacker-controlled branch to become the new default. In repositories that required pull-request review but did not restrict branch deletion, this bypassed the review requirement and caused fresh clones and default-branch API requests to use attacker-controlled content. This vulnerability affected supported GitHub Enterprise Server releases in the 3.18, 3.19, 3.20, 3.21, and 3.22 series and was fixed in versions 3.18.16, 3.19.13, 3.20.9, 3.21.7, and 3.22.2. This vulnerability was reported via the GitHub Bug Bounty program.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2026-103620?

It affects 1 product.


Products: Github Enterprise Server.

## How do I fix CVE-2026-103620?

No fix has been published for CVE-2026-103620 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-103620 being exploited?

There is no known exploitation of CVE-2026-103620 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-2026-103620 and fix it if it is affected.

What it is: CVE-2026-103620 is a medium-severity missing authorization vulnerability in Github Enterprise Server, published on 6 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-103620 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-2026-103620/ (Markdown: https://insights.sbomify.com/CVE-2026-103620/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-103620
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-103620
- OSV: https://osv.dev/vulnerability/CVE-2026-103620

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-103620/
Summaries are generated and may contain mistakes; the official description above is the record.