CVE-2026-26061: 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.
Other sources
Fleet is open source device management software. Prior to 4.81.0, 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. Version 4.81.0 patches the issue.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-26061?
CVE-2026-26061 is classified as a denial of service vulnerability due to its potential to crash services by overwhelming them with large payloads.
How do I fix CVE-2026-26061?
To fix CVE-2026-26061, update Fleet to version 4.43.5-0.20260113202849-bbc1aef2987d or later, where the issue has been addressed.
What kind of attacks can CVE-2026-26061 facilitate?
CVE-2026-26061 can facilitate denial of service attacks by allowing attackers to send unbounded request bodies, overwhelming server resources.
Which versions of Fleet are affected by CVE-2026-26061?
Versions of Fleet prior to 4.43.5-0.20260113202849-bbc1aef2987d are affected by CVE-2026-26061.
Is authentication required to exploit CVE-2026-26061?
No, CVE-2026-26061 can be exploited without authentication, allowing any unauthenticated attacker to trigger the vulnerability.