CVE-2026-126401: Fleet before 4.86.2 Unauthenticated DoS via SSO Callback XML Canonicalization
fleetdm · fleet
Fixed in 4.86.2 · Affected: fleetdm before 4.86.2 · Exploitation: unlikely (under 1%)
Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.
Higher than 44% of scored CVEs
DescriptionCVE.org
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.
Affected products1
From the CVE record. A product or version that is not listed is unknown, not unaffected.
- fleetdm · fleetbefore 4.86.2
On the Atlas
Every published CVE is on the CyberSIXT Atlas, grouped by weakness, vendor and month.
- Exploitation
- Unlikely (under 1%). EPSS under 1%, or no score yet.
- CISA KEV
- Not listed
- Public check
- No public nuclei template
- Vendor
- fleetdm
- Published
- November 2026
CoverageNo articles yet
No CyberSIXT article names CVE-2026-126401 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.