CVE-2026-46356: Fleet: IP spoofing allows bypassing API rate limiting
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
Credits We thank @fuzzztf for responsibly reporting this issue.
Other sources
Fleet is open source device management software. Prior to version 4.80.1, 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. 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. Version 4.80.1 contains a patch. 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.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-46356?
CVE-2026-46356 is considered a critical vulnerability due to its potential for facilitating brute-force login attempts against Fleet instances.
How do I fix CVE-2026-46356?
To fix CVE-2026-46356, upgrade Fleet to version 4.80.1 or later to mitigate the risk of IP spoofing.
What systems are affected by CVE-2026-46356?
CVE-2026-46356 affects all versions of Fleet prior to 4.80.1.
What type of attack does CVE-2026-46356 expose systems to?
CVE-2026-46356 exposes systems to attacks such as brute-force login attempts by bypassing API rate limiting.
Is authentication required to exploit CVE-2026-46356?
No, CVE-2026-46356 can be exploited by unauthenticated attackers through spoofed client IP headers.