---
id: "CVE-2026-126401"
page: "https://infrastack.ai/live/CVE-2026-126401"
kind: "vulnerability"
aliases: ["CVE-2026-126401"]
title: "Fleet: unsigned SAML response exhausts server memory and crashes it"
severity: "high"
cvss: 8.7
epss: null
exploited: false
status: "open"
category: "other"
products: [{"name": "fleet", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["fleet", "other", "saml-sso", "self-hosted"]
not_affected_if: ["fleet-4.86.2-or-later", "no-saml-sso"]
published_at: "2026-11-13T10:17:44+00:00"
first_seen_at: "2026-11-13T10:47:19+00:00"
updated_at: "2026-11-13T10:50:24+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-126401", "first_seen_at": "2026-11-13T10:47:19+00:00"}]
exploit_sources: []
---

# Fleet: unsigned SAML response exhausts server memory and crashes it

Link for people: https://infrastack.ai/live/CVE-2026-126401 (this .md is for agents)

Fleet, a device management server, can be crashed by one specially crafted SAML response sent to its SSO callback endpoint. The flaw lets an unauthenticated attacker exhaust server memory, causing a denial of service.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:fleet affected range not listed fixed no fixed version listed

## How to check

- Check the installed Fleet server version and compare it with `4.86.2`.
- Look for SSO (SAML) being enabled on the Fleet server, which exposes POST /api/v1/fleet/sso/callback.

## Fix

- Fleet versions before `4.86.2` are affected; move to `4.86.2` or later.

## Timeline

- 2026-11-13T10:47:19+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-126401

## Documents

- [advisory] Vendor advisory: github.com https://github.com/fleetdm/fleet/security/advisories/GHSA-mjrh-3v6h-8g5p
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/fleet-before-4.86.2-unauthenticated-dos-via-sso-callback-xml-canonicalization

## From the sources

Fleet before 4.86.2 contains a denial of service vulnerability that allows unauthenticated attackers to exhaust server memory through quadratic XML canonicalization of unsigned SAML responses. Attackers can send a single crafted SAML response with deeply nested elements declaring new namespace prefixes to POST /api/v1/fleet/sso/callback, crashing the Fleet server.

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_