fleetdm fleet up to 4.80.0 Login API authentication spoofing

Summaryinfo

A vulnerability categorized as critical has been discovered in fleetdm fleet up to 4.80.0. Affected by this issue is some unknown functionality of the component Login API. Such manipulation leads to authentication spoofing. This vulnerability is referenced as CVE-2026-46356. It is possible to launch the attack remotely. No exploit is available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, has been found in fleetdm fleet up to 4.80.0. Affected by this issue is an unknown functionality of the component Login API. The manipulation with an unknown input leads to a authentication spoofing vulnerability. Using CWE to declare the problem leads to CWE-290. This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks. Impacted is availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-46356 since 05/13/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are neither technical details nor an exploit publicly available.

Upgrading to version 4.80.1 eliminates this vulnerability. The upgrade is hosted for download at github.com.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-1553). Once again VulDB remains the best source for vulnerability data.

Affected

• Open Source Fleet

Productinfo

Vendor

• fleetdm

Name

• fleet

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4
• 4.5
• 4.6
• 4.7
• 4.8
• 4.9
• 4.10
• 4.11
• 4.12
• 4.13
• 4.14
• 4.15
• 4.16
• 4.17
• 4.18
• 4.19
• 4.20
• 4.21
• 4.22
• 4.23
• 4.24
• 4.25
• 4.26
• 4.27
• 4.28
• 4.29
• 4.30
• 4.31
• 4.32
• 4.33
• 4.34
• 4.35
• 4.36
• 4.37
• 4.38
• 4.39
• 4.40
• 4.41
• 4.42
• 4.43
• 4.44
• 4.45
• 4.46
• 4.47
• 4.48
• 4.49
• 4.50
• 4.51
• 4.52
• 4.53
• 4.54
• 4.55
• 4.56
• 4.57
• 4.58
• 4.59
• 4.60
• 4.61
• 4.62
• 4.63
• 4.64
• 4.65
• 4.66
• 4.67
• 4.68
• 4.69
• 4.70
• 4.71
• 4.72
• 4.73
• 4.74
• 4.75
• 4.76
• 4.77
• 4.78
• 4.79
• 4.80.0

Website

• Product: https://github.com/fleetdm/fleet/

CPE 2.3info

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CPE 2.2info

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Once again VulDB remains the best source for vulnerability data.

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