PT-2026-40979 · Go · Github.Com/Fleetdm/Fleet
Published
2026-05-14
·
Updated
2026-05-14
·
CVE-2026-46356
CVSS v4.0
6.9
Medium
| Vector | AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N |
Summary
A vulnerability in Fleet's IP extraction logic allows unauthenticated attackers to bypass API rate limiting by spoofing client IP headers. This may allow brute-force login attempts or other abuse against Fleet instances exposed to the public internet.
Impact
Fleet extracted client IP addresses from request headers (
True-Client-IP, X-Real-IP, X-Forwarded-For) without validating that those headers originate from a trusted proxy. The extracted IP is used as the key for rate limiting and IP ban decisions.As a result, an attacker could rotate the value of these headers on each request, causing Fleet to treat each attempt as coming from a different client. This effectively bypasses per-IP rate limits on sensitive endpoints such as the login API, enabling unrestricted brute-force or credential stuffing attacks.
This issue primarily affects Fleet instances that are directly exposed to the internet without a reverse proxy that overwrites forwarded-IP headers. Instances behind a properly configured proxy or WAF are less affected.
Workarounds
If an immediate upgrade is not possible, administrators should ensure Fleet is deployed behind a reverse proxy (e.g., nginx, Cloudflare, AWS ALB) that overwrites
X-Forwarded-For with the true client IP, and apply rate limiting at the proxy or WAF layer.For more information
If you have any questions or comments about this advisory:
Email us at security@fleetdm.com
Join #fleet in [osquery Slack](https://join.slack.com/t/osquery/shared invite/zt-h29zm0gk-s2DBtGUTW4CFel0f0IjTEw)
Credits
We thank @fuzzztf for responsibly reporting this issue.
Fix
Authentication Bypass by Spoofing
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Weakness Enumeration
Related Identifiers
Affected Products
Github.Com/Fleetdm/Fleet