CVE-2026-23998 — v4
Fix: fleetdm/fleet@3ff8119CVE-2026-23998 is a CWE-295 vulnerability in github.com/fleetdm/fleet/v4. A fix is available for github.com/fleetdm/fleet/v4 — see the affected versions and patch details below.
Fleet has a Windows MDM management endpoint authentication bypass
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-23998.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
github.com/fleetdm/fleet/v4Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Summary
A vulnerability in Fleet’s Windows MDM management endpoint could allow requests to be processed without proper client certificate validation. In certain circumstances, this could allow an attacker to impersonate an enrolled Windows device and retrieve sensitive configuration data.
Impact
Fleet’s Windows MDM management endpoint relies on mutual TLS (mTLS) client certificates to authenticate enrolled devices. In affected versions, requests that did not present a client certificate could be incorrectly treated as trusted.
As a result, an attacker with prior knowledge of a valid enrolled device identifier could potentially impersonate that device and receive configuration payloads intended for it. These payloads may contain sensitive information such as Wi-Fi or VPN configuration data, certificates, or other secrets delivered through MDM profiles.
This issue does not allow enrollment of new devices, administrative access to Fleet, or compromise of the Fleet control plane. Impact is limited to the targeted Windows device.
Workarounds
If an immediate upgrade is not possible, affected Fleet users should temporarily disable Windows MDM.
For more information
If you have any questions or comments about this advisory:
Email us at [email protected] Join #fleet in osquery Slack
Credits
We thank @secfox-ai for responsibly reporting this issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/fleetdm/fleet/v4 | all versions | 4.81.0go get github.com/fleetdm/fleet/v4@v4.81.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/fleetdm/fleet/v4, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/fleetdm/fleet/v4 to 4.81.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-23998 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-23998 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-23998. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-23998 in your dependencies?
O3 Security finds CVE-2026-23998 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.