CVE-2026-46356: Fleet IP Spoofing Allows Bypassing API Vulnerability

MODERATE
Advisory Identifier: GHSA-mxmp-wr3w-rvqx
Share
CWE-290
Published
Advisory Summary

CVE-2026-46356 is a MODERATE ip spoofing allows bypassing api vulnerability (CWE-290: Authentication Bypass by Spoofing) affecting Fleet libraries in the Go ecosystem. The issue involves ip spoofing allows bypassing api rate limiting. Remediation is available by upgrading affected packages to version 4.80.1.

CVE-2026-46356 at a Glance

CVE Identifier CVE-2026-46356
GHSA Identifier GHSA-mxmp-wr3w-rvqx
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-290: Authentication Bypass by Spoofing
Affected Product Fleet
Package Ecosystem Go
Published Date
Last Updated

How to Fix CVE-2026-46356

To remediate this vulnerability, upgrade all affected Fleet dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/fleetdm/fleet/v4 fixed: 4.80.1 
Upgrade github.com/fleetdm/fleet/v4 to 4.80.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/fleetdm/fleet/v4

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-46356, inspect your project dependencies for Fleet:

inspect dependencies for github.com/fleetdm/fleet/v4

Analyze the terminal output to locate any version of Fleet in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.80.1), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-290: Authentication Bypass by Spoofing, where this attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks. In Fleet, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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](mailto: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.

CVE-2026-46356 Affected Fleet Versions

1 component(s)
Fixed Versions:
4.80.1
Product / Package Ecosystem Affected Versions Fixed Version
github.com/fleetdm/fleet/v4
golang/github.com/fleetdm/fleet/v4
Go
< 4.80.1
4.80.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/fleetdm/fleet/security/advisories/GHSA-mxmp-wr3w-rvqx
NVD — CVE-2026-46356 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-46356
Fleet Source Repository REPOSITORY
https://github.com/fleetdm/fleet
Fleet Release RELEASE
https://github.com/fleetdm/fleet/releases/tag/fleet-v4.80.1

Frequently Asked Questions

What is CVE-2026-46356?
CVE-2026-46356 is a security vulnerability in Fleet involving IP spoofing allows bypassing API rate limiting under CWE-290: Authentication Bypass by Spoofing.
Which Fleet versions are affected?
Affected versions include releases prior to 4.80.1 across affected packages: github.com/fleetdm/fleet/v4.
What version fixes CVE-2026-46356?
Upgrading to 4.80.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/fleetdm/fleet/v4 affected?
Yes, github.com/fleetdm/fleet/v4 is affected in releases prior to 4.80.1. Upgrade your dependency to 4.80.1 or later.
What CWE is associated with CVE-2026-46356?
CVE-2026-46356 is classified under CWE-290: Authentication Bypass by Spoofing (This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.).
How can I check Go dependencies for CVE-2026-46356?
Run the dependency tree command: 'inspect dependencies for github.com/fleetdm/fleet/v4'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mxmp-wr3w-rvqx",
  "modified" : "2026-05-15T23:45:48Z",
  "published" : "2026-05-14T13:18:33Z",
  "aliases" : [ "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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/fleetdm/fleet/v4"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.80.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "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"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fleetdm/fleet/releases/tag/fleet-v4.80.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-290" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-14T13:18:33Z",
    "nvd_published_at" : "2026-05-14T20:17:09Z"
  }
}