Summary
Fleet's user account creation via invite does not enforce invited email address
Fleet contained an issue in the user invitation flow where the email address provided during invite acceptance was not validated against the email address associated with the invite. An attacker who obtained a valid invite token could create an account under an arbitrary email address while inheriting the role granted by the invite, including global admin.
Workarounds
If upgrading immediately is not possible:
- Treat invite links as sensitive credentials and avoid sharing them in public or semi-public channels (e.g., Slack, Teams).
- Revoke and reissue invites if there is any concern that an invite link may have been exposed.
- Prefer issuing invites with the minimum required privileges and elevating roles after account creation when appropriate.
For more information
If there are any questions or comments about this advisory:
Send an email to [email protected]
Credits
Fleet thanks @fuzzztf for responsibly reporting this issue.
Impact
If an attacker gains access to a valid invite token, they can create a Fleet user account with an email address of their choosing while inheriting the invite’s assigned role and team memberships.
This issue:
- Requires possession of a valid invite token
- Does not bypass authentication controls beyond invite-based account creation
- Does not expose data without successful account creation
The application does not adequately verify the identity of a user, device, or process before granting access. Typical impact: unauthorized access to functions or data reserved for authenticated parties.
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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Frequently Asked Questions
- What is CVE-2026-34389? CVE-2026-34389 is a medium-severity improper authentication vulnerability in github.com/fleetdm/fleet/v4 (go), affecting versions < 4.81.0. It is fixed in 4.81.0. The application does not adequately verify the identity of a user, device, or process before granting access.
- Which versions of github.com/fleetdm/fleet/v4 are affected by CVE-2026-34389? github.com/fleetdm/fleet/v4 (go) versions < 4.81.0 is affected.
- Is there a fix for CVE-2026-34389? Yes. CVE-2026-34389 is fixed in 4.81.0. Upgrade to this version or later.
- Is CVE-2026-34389 exploitable, and should I be worried? Whether CVE-2026-34389 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-2026-34389 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-2026-34389? Upgrade
github.com/fleetdm/fleet/v4to 4.81.0 or later.