Fleet's unbounded request body read allows remote Denial of Service

Summary

Fleet contained multiple unauthenticated HTTP endpoints that read request bodies without enforcing a size limit. An unauthenticated attacker could exploit this behavior by sending large or repeated HTTP payloads, causing excessive memory allocation and resulting in a denial-of-service (DoS) condition.

Impact

An unauthenticated attacker could cause the Fleet server process to exhaust available memory and restart by sending oversized or repeated HTTP requests to affected endpoints.

This vulnerability impacts availability only. There is:

• No exposure of sensitive data
• No authentication bypass
• No privilege escalation
• No integrity impact

Workarounds

If upgrading immediately is not possible, the following mitigations can reduce exposure:

• Apply request body size limits at a reverse proxy or load balancer (e.g., NGINX, Envoy).
• Restrict network access to endpoints to known IP ranges where feasible.
• Monitor memory usage and restart frequency for abnormal patterns.

For More Information

If there are any questions or concerns about this advisory, please contact us at:

Email Fleet at security@fleetdm.com

Credits

Fleet thanks @fuzzztf for responsibly reporting this issue.