Summary
Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment
A vulnerability in Fleet’s Windows MDM enrollment flow could allow an attacker to submit forged authentication tokens that are not properly validated. Because JWT signatures were not verified, Fleet could accept attacker-controlled identity claims, enabling enrollment of unauthorized devices under arbitrary Azure AD user identities.
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:
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Credits
We thank @secfox-ai for responsibly reporting this issue.
Impact
If Windows MDM is enabled, an attacker can enroll rogue devices by submitting a forged JWT containing arbitrary identity claims. Due to missing JWT signature verification, Fleet accepts these claims without validating that the token was issued by Azure AD, allowing enrollment under any Azure AD user identity.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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- 4.78.3
- 4.77.1
- 4.76.2
- 4.75.2
- 4.53.3
Frequently Asked Questions
- What is CVE-2026-23518? CVE-2026-23518 is a critical-severity security vulnerability in github.com/fleetdm/fleet (go), affecting versions >= 4.78.0, < 4.78.3. It is fixed in 4.78.3, 4.77.1, 4.76.2, 4.75.2, 4.43.5-0.20260112202845-e225ef57912c.
- Which versions of github.com/fleetdm/fleet are affected by CVE-2026-23518? github.com/fleetdm/fleet (go) versions >= 4.78.0, < 4.78.3 is affected.
- Is there a fix for CVE-2026-23518? Yes. CVE-2026-23518 is fixed in 4.78.3, 4.77.1, 4.76.2, 4.75.2, 4.43.5-0.20260112202845-e225ef57912c. Upgrade to this version or later.
- Is CVE-2026-23518 exploitable, and should I be worried? Whether CVE-2026-23518 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-23518 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-23518?
- Upgrade
github.com/fleetdm/fleetto 4.78.3 or later - Upgrade
github.com/fleetdm/fleetto 4.77.1 or later - Upgrade
github.com/fleetdm/fleetto 4.76.2 or later - Upgrade
github.com/fleetdm/fleetto 4.75.2 or later - Upgrade
github.com/fleetdm/fleetto 4.43.5-0.20260112202845-e225ef57912c or later
- Upgrade