⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● High · CVSS 7.1

How to Fix CVE-2026-1999: Access Control Bypass in Enterprise Server

Other vulnerabilities in the same area that are worth patching alongside this one:

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityCVSS 7.1 - High
Actively exploited?Not currently listed in CISA KEV
Affected3.17.0 < 3.17.11, 3.18.0 < 3.18.5, 3.19.0 < 3.19.2
Fixed inversions
Type (CWE)CWE-863: Incorrect Authorization

What is CVE-2026-1999?

CVE-2026-1999 is an access control bypass flaw in Enterprise Server. Authenticated or in some cases unauthenticated requests reach endpoints they should not be allowed to call, exposing administrative functionality or sensitive data. Vendor description: An 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.

Why this CVE matters

Access control flaws let an attacker reach endpoints the developers assumed would be reserved for administrators. The impact depends on what those endpoints expose, but for management products the answer is usually configuration changes, log access, or credential reads.

For deployments of Enterprise Server that have been exposed to the public internet during the disclosure window, the operating assumption should be that scanning has already happened. Even where exploitation has not been publicly observed, scanning for the vulnerable fingerprint is cheap and routine. Patching closes the door; log review and credential rotation close out the rest of the response.

Am I affected?

You are affected if your installation matches any of these version ranges:

Check your installed version against the list above. If you cannot determine the version, treat the system as affected and follow the upgrade path below.

Run git --version to confirm the installed Git release and compare against the affected ranges.

How to fix CVE-2026-1999

  1. Read the vendor advisory in full: https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.11
  2. Upgrade Enterprise Server to the patched build listed in the vendor advisory.
  3. Back up the configuration (and database, where applicable) before upgrading.
  4. Apply the patch in a maintenance window. For HA pairs, upgrade the standby node first, fail over, then upgrade the former primary.
  5. Restart the affected service so the patched binary loads, then verify the new version (see verification section).

npm / Yarn / pnpm


# Confirm the patched build against the vendor advisory: https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.11
# Update to the patched release 3.17.11.
npm install enterprise-server@3.17.11
# Alternative pinning:
npm install enterprise-server@latest
npm ls enterprise-server

PyPI (pip / Poetry)


# Confirm the patched build against the vendor advisory: https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.11
pip install --upgrade "enterprise-server==3.17.11"
pip show enterprise-server | grep -i version

# Poetry equivalent:
poetry add enterprise-server@3.17.11

Docker / container


# Confirm the patched build against the vendor advisory: https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.11
docker pull <your-registry>/enterprise-server:3.17.11
docker stop <app> && docker rm <app>
docker run -d --name <app> <your-registry>/enterprise-server:3.17.11
docker image inspect <your-registry>/enterprise-server:3.17.11 --format '{{.Id}}'

Ubuntu / Debian


# Confirm the patched build against the vendor advisory: https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.11
sudo apt-get update
sudo apt-get install --only-upgrade git
dpkg -s git | grep -i version
# Target patched version: 3.17.11

RHEL / Rocky / AlmaLinux / Fedora


# Confirm the patched build against the vendor advisory: https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.11
sudo dnf upgrade --refresh git -y
rpm -q git
# Target patched version: 3.17.11

openSUSE


sudo zypper refresh
sudo zypper update git

Verify the fix landed


# Confirm the patched build against the vendor advisory: https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.11
# 1. Confirm the running version equals the advisory's fixed-in build.
#    (Use the platform-specific version probe from the commands above.)

# 2. Re-scan with your vulnerability scanner (Nessus, Qualys, Tenable, OpenVAS).
#    The scanner should no longer flag CVE-2026-1999 on the patched target.

# 3. Inspect recent service and kernel logs for crash-loops or rollback events.
journalctl --since "10 minutes ago" | tail -200
dmesg --since "10 minutes ago" | tail -100

If you cannot patch immediately

No official workaround exists beyond restricting network exposure to the affected component. Apply the vendor patch as the primary remediation.

How to verify the fix worked

If your installation was internet-reachable during the disclosure window, treat log review as part of the remediation rather than an optional follow-up. Look for log entries that do not match your normal request patterns, especially repeated requests to the same uncommon endpoint, and any administrative changes you cannot tie back to a known operator.

Frequently asked questions

Is CVE-2026-1999 being exploited in the wild?

Public exploitation has not been confirmed by CISA at the time of writing. Treat the patch as time-sensitive anyway; reports often lag actual abuse.

Will a WAF or IDS rule fully mitigate CVE-2026-1999?

No. Network-layer filters can reduce noise and slow opportunistic scanners, but they will not stop a determined attacker. The vendor patch is the only durable fix.

How long should I plan for the upgrade?

Typical vendor-documented upgrade windows for Enterprise Server run from a few minutes to under an hour depending on cluster size. Test in a staging environment first and follow the vendor's documented HA upgrade order.

References

*This guide was assembled from the official vendor advisory, the NVD record, and the CISA KEV catalog entry on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*