CVE-2026-34388: Fleet vulnerable to Denial of Service via unhandled gRPC log type in launcher endpoint
Summary
A Denial of Service vulnerability in Fleet's gRPC Launcher endpoint allows an authenticated host to crash the entire Fleet server process by sending an unexpected log type value. The server terminates immediately, disrupting all connected hosts, MDM enrollments, and API consumers.
Impact
An attacker with access to a valid Launcher node key can send a specially crafted gRPC request to the Fleet server that triggers an unrecoverable server crash. The gRPC server lacks appropriate error recovery handling, meaning the entire Fleet process terminates rather than gracefully rejecting the malformed input.
Because the crash is instant and repeatable, an attacker could script repeated requests to prevent the server from recovering, resulting in a persistent denial of service until a patched version is deployed.
Workarounds
There is no workaround for this issue other than upgrading to a patched version.
For more information
If there are any questions or comments about this advisory:
Send an email to security@fleetdm.com
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Credits
Fleet thanks @fuzzztf for responsibly reporting this issue.
Other sources
Fleet is open source device management software. Prior to 4.81.0, a denial-of-service vulnerability in Fleet's gRPC Launcher endpoint allows an authenticated host to crash the entire Fleet server process by sending an unexpected log type value. The server terminates immediately, disrupting all connected hosts, MDM enrollments, and API consumers. Version 4.81.0 patches the issue.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-34388?
CVE-2026-34388 is classified as a Denial of Service vulnerability that can lead to the crashing of the Fleet server.
How do I fix CVE-2026-34388?
To mitigate CVE-2026-34388, upgrade Fleet to version 4.81.0 or later.
Who is affected by CVE-2026-34388?
CVE-2026-34388 affects all versions of Fleet prior to 4.81.0.
What causes CVE-2026-34388?
CVE-2026-34388 is caused by the handling of unexpected log type values in the gRPC Launcher endpoint.
Can CVE-2026-34388 be exploited remotely?
CVE-2026-34388 requires authentication, thus it cannot be exploited by unauthenticated users.