What’s Vulnerable › Vulnerabilities

CVE-2020-26276: SAML authentication vulnerability in Fleet

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-12-17 · updated 2026-06-17
• Weakness: CWE-290

Description

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.

Affected products

• fleetdm fleet: before 3.5.1 — fixed in 3.5.1

How to fix

Upgrade to a fixed version: fleetdm fleet 3.5.1. Check the vendor advisory for mitigations.

References

• https://github.com/fleetdm/fleet/blob/master/CHANGELOG.md#fleet-351-dec-14-2020
• https://github.com/fleetdm/fleet/commit/57812a532e5f749c8e18c6f6a652eca65c083607
• https://github.com/fleetdm/fleet/security/advisories/GHSA-w3wf-cfx3-6gcx
• https://github.com/mattermost/xml-roundtrip-validator
• https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities
• https://github.com/fleetdm/fleet/blob/master/CHANGELOG.md#fleet-351-dec-14-2020
• https://github.com/fleetdm/fleet/commit/57812a532e5f749c8e18c6f6a652eca65c083607
• https://github.com/fleetdm/fleet/security/advisories/GHSA-w3wf-cfx3-6gcx
• https://github.com/mattermost/xml-roundtrip-validator
• https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities

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