SAML authentication vulnerability in Fleet
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Security bypass
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-290.
Summary
Fleet is an open source osquery manager. In Fleet before version 3.5.1, due to issues in Go's standard library XML parsing, a valid SAML response may be mutated by an attacker to modify the trusted document. This can result in allowing unverified logins from a SAML IdP. Users that configure Fleet with SSO login may be vulnerable to this issue. This issue is patched in 3.5.1. The fix was made using https://github.com/mattermost/xml-roundtrip-validator If upgrade to 3.5.1 is not possible, users should disable SSO authentication in Fleet.
Why it matters now
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| fleetdm | fleet | before 3.5.1 | 3.5.1 | Patch available | CNA |
| — | github.com/fleetdm/fleet/v4 (Go) | before 3.5.1 | 3.5.1 | Patch available | GHSA-w3wf-cfx3-6gcx |
- fleet Vendorfleetdm Affected before 3.5.1 Fixed in 3.5.1 Patch available CNA
- github.com/fleetdm/fleet/v4 (Go) Vendor— Affected before 3.5.1 Fixed in 3.5.1 Patch available GHSA-w3wf-cfx3-6gcx
Remediation
- Fix · CNA fleet (fleetdm) Fixed in 3.5.1
- Fix · GHSA-w3wf-cfx3-6gcx github.com/fleetdm/fleet/v4 (Go) Fixed in 3.5.1 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2020-26276
- 2026-10-03 Alias added: GHSA-w3wf-cfx3-6gcx
References
Advisory 5
- https://github.com/fleetdm/fleet/security/advisories/GHSA-w3wf-cfx3-6gcx
- https://github.com/fleetdm/fleet/blob/master/CHANGELOG.md#fleet-351-dec-14-2020
- https://github.com/mattermost/xml-roundtrip-validator
- https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities
- https://nvd.nist.gov/vuln/detail/CVE-2020-26276
More fleetdm Fleet vulnerabilities
- TI-2026-65639 Fleet before 4.87.0 Authentication Bypass via Device Identifiers CVSS 4.0CRITICAL 9.3
- TI-2026-18942 Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment CVSS 4.0CRITICAL 9.3
- TI-2026-21066 Fleet server may terminate unexpectedly when handling certain gRPC requests CVSS 4.0HIGH 8.7
- TI-2026-21065 Fleet's unbounded request body read allows remote Denial of Service CVSS 4.0HIGH 8.7
- TI-2026-20084 Fleet Windows MDM Azure AD JWT Authentication Bypass CVSS 4.0HIGH 8.2
- TI-2026-19339 Fleet has a rate limiting bypass via untrusted client IP headers CVSS 4.0MEDIUM 6.9
Sources
- CVE-2020-26276 · CVE Program
- CVE-2020-26276 · NVD
- FIRST EPSS
- GHSA-w3wf-cfx3-6gcx · GitHub Advisory Database · CC BY 4.0
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