CVE-2026-26061 — v4
CVE-2026-26061 is a CWE-770 vulnerability in github.com/fleetdm/fleet/v4. A fix is available for github.com/fleetdm/fleet/v4 — see the affected versions and patch details below.
Fleet's unbounded request body read allows remote Denial of Service
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-26061.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
github.com/fleetdm/fleet/v4Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
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 [email protected]
Credits
Fleet thanks @fuzzztf for responsibly reporting this issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/fleetdm/fleet/v4 | all versions | 4.43.5-0.20260113202849-bbc1aef2987dgo get github.com/fleetdm/fleet/v4@v4.43.5-0.20260113202849-bbc1aef2987d |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/fleetdm/fleet/v4, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/fleetdm/fleet/v4 to 4.43.5-0.20260113202849-bbc1aef2987d or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-26061 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-26061 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-26061. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-26061 in your dependencies?
O3 Security finds CVE-2026-26061 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.