{"id":"CVE-2026-46356","aliases":["GHSA-mxmp-wr3w-rvqx","GO-2026-5520"],"url":"https://o3.security/vulnerability/CVE-2026-46356","summary":"Fleet: IP spoofing allows bypassing API rate limiting","details":"### Summary\nA 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.\n\n### Impact\nFleet 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.\n\nAs 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.\n\nThis 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.\n\n### Workarounds\nIf 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.\n\n### For more information\nIf you have any questions or comments about this advisory:\nEmail us at [security@fleetdm.com](mailto:security@fleetdm.com)\nJoin #fleet in [osquery Slack](https://join.slack.com/t/osquery/shared_invite/zt-h29zm0gk-s2DBtGUTW4CFel0f0IjTEw)\n\n### Credits\nWe thank @fuzzztf for responsibly reporting this issue.","published":"2026-05-14T19:03:50.754Z","modified":"2026-08-12T03:51:28.035594493Z","cvss":null,"epss":{"score":0.00276,"percentile":0.19481,"asOf":"2026-08-24"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/fleetdm/fleet/v4","fixedVersion":"4.80.1"}],"fix":null,"references":[{"type":"WEB","url":"https://github.com/fleetdm/fleet/releases/tag/fleet-v4.80.1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46356.json"},{"type":"ADVISORY","url":"https://github.com/fleetdm/fleet/security/advisories/GHSA-mxmp-wr3w-rvqx"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-46356"},{"type":"PACKAGE","url":"https://github.com/fleetdm/fleet"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:28.035594493Z"}}