Enterprise ServerApplication · GitHub
CVE-2026-1999
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedAn incorrect authorization vulnerability was identified in GitHub Enterprise Server that allowed an attacker to merge their own pull request into a repository without having push access by exploiting an authorization bypass in the enable_auto_merge mutation for pull requests. This issue only affected repositories that allow forking as the attack relies on opening a pull request from an attacker-controlled fork into the target repository. Exploitation was only possible in specific scenarios. It required a clean pull request status and only applied to branches without branch protection rules enabled. This vulnerability affected GitHub Enterprise Server versions prior to 3.19.2, 3.18.5, and 3.17.11, and was fixed in versions 3.19.2, 3.18.5, and 3.17.11. This vulnerability was reported via the GitHub Bug Bounty program.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceAn authorization bypass in GitHub Enterprise Server's enable_auto_merge mutation allowed attackers to merge pull requests from their own forks into target repositories without having push access. The attack exploited the fork-based pull request workflow and required specific conditions: clean PR status and branches without branch protection rules enabled.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Enterprise ServerApplication
< 3.17.11>= 3.18.0, < 3.18.5>= 3.19.0, < 3.19.2CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify your GitHub Enterprise Server versionAccess the GitHub Enterprise Server admin console or run 'ghe-version' from the management shell. The version is also visible in the site admin dashboard footer.Affected if The installed version falls into any of these ranges: < 3.17.11, >= 3.18.0 to < 3.18.5, or >= 3.19.0 to < 3.19.2
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Review branch protection rules on target repositoriesNavigate to each repository's Settings > Branches section in the web UI, or query the GitHub API endpoint /repos/{owner}/{repo}/branches/{branch}/protection for each critical branch.Affected if No branch protection rules are defined, or branch protection rules exist but do not enforce required status checks or require pull request reviews before merging
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Verify pull request auto-merge configurationCheck if the 'Allow auto-merge' setting is enabled in repository settings (Settings > General > Pull requests). This setting allows the enable_auto_merge mutation to be used.Affected if Auto-merge is enabled on repositories with unprotected branches, creating the condition for the vulnerability to be exploited
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Audit recent enable_auto_merge mutationsQuery the GitHub audit log for events containing 'enable_auto_merge' action, filtering for events where the pull request originates from a fork (different repository owner). Use the enterprise or organization audit log API.Affected if Audit logs show enable_auto_merge actions performed on pull requests from external forks that merged without the actor having push access to the target branch
You are affected if your GHES version is in the vulnerable ranges AND your repositories have branches without branch protection rules while auto-merge is enabled.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped3.17.113.18.53.19.2
Upgrade GitHub Enterprise Server to version 3.19.2, 3.18.5, or 3.17.11 or later. Additionally, enable branch protection rules on critical branches as a defense-in-depth measure.
Upgrade to 3.17.11 (or later 3.17.x), 3.18.5 (or later 3.18.x), or 3.19.2 (or later 3.19.x) depending on your current major version line
- 1. Identify current GitHub Enterprise Server version via the administrative web UI (Site Admin > Management Console > Version) or admin shell (ghe-version).
- 2. Determine the appropriate upgrade path based on current version: if < 3.17.11, upgrade to 3.17.11 or later in the 3.17.x line; if >= 3.18.0 and < 3.18.5, upgrade to 3.18.5 or later in the 3.18.x line; if >= 3.19.0 and < 3.19.2, upgrade to 3.19.2 or later in the 3.19.x line.
- 3. Review GitHub Enterprise Server upgrade documentation and create a backup/snapshot of the current instance before upgrading.
- 4. Perform the upgrade following standard GitHub Enterprise Server upgrade procedures for your deployment method (hotpatch or full upgrade).
- 5. After upgrade, verify the version matches the expected fixed release and confirm GitHub Enterprise Server is operational.
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Enterprise Server
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,120.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-1999 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-1999 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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