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CVE-2026-126401 Fleet before 4.86.2 Unauthenticated DoS via SSO Callback XML Canonicalization

8.7 highEPSS 0.5%

High (8.7) in fleetdm fleet. EPSS 0.5% estimated probability of exploitation activity in the next 30 days.

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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.

Severity

CVSS 4.0

8.7 high
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

CVSS 3.1

7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
0.5% estimated probability of exploitation activity in the next 30 days; 44th percentile. Scored 2026-11-13. A forecast for this CVE across the internet, not for your own systems.
CWE
CWE-407 Inefficient Algorithmic Complexity
Published
Assigned by
VulnCheck (CNA)
NVD analysis
Awaiting analysis
Record from
the NVD, synced

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Affected

Versions

From the CNA's record in the CVE List.

ProductAffected
fleetdm fleetbefore 4.86.2

References

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