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.

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact None

Vulnerable System Availability Impact High

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
fleetdm fleet unaffected
Version Status Constraints
0 affected < 4.86.2
4.86.2 unaffected —

No data.

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Project Subscriptions

Vendors Products
Fleetdm Subscribe
Fleet Subscribe
Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/fleetdm/fleet/security/advisories/GHSA-mjrh-3v6h-8g5p cve-icon cve-icon
https://www.vulncheck.com/advisories/fleet-before-4.86.2-unauthenticated-dos-via-sso-callback-xml-canonicalization cve-icon cve-icon
History

Fri, 13 Nov 2026 09:45:00 +0000

Type Values Removed Values Added
Description 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.
Title Fleet before 4.86.2 Unauthenticated DoS via SSO Callback XML Canonicalization
First Time appeared Fleetdm
Fleetdm fleet
Weaknesses CWE-407
CPEs cpe:2.3:a:fleetdm:fleet:*:*:*:*:*:*:*:*
Vendors & Products Fleetdm
Fleetdm fleet
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

cvssV4_0

{'score': 8.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-11-13T09:35:47.679Z

Reserved: 2026-11-10T21:32:21.765Z

Link: CVE-2026-126401

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-11-13T10:17:44.597

Modified: 2026-11-13T10:17:44.597

Link: CVE-2026-126401

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses