{"id":"CVE-2020-26276","aliases":["GHSA-w3wf-cfx3-6gcx"],"url":"https://o3.security/vulnerability/CVE-2020-26276","summary":"SAML authentication vulnerability due to stdlib XML parsing","details":"### Impact\nDue 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.\n\nUsers that configure Fleet with SSO login may be vulnerable to this issue.\n\n### Patches\nThis issue is patched in 3.5.1 using https://github.com/mattermost/xml-roundtrip-validator.\n\n### Workarounds\nIf upgrade to 3.5.1 is not possible, users should disable SSO authentication in Fleet.\n\n### References\nSee https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities/ for more information about the underlying vulnerabilities.\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Email us at [security@fleetdm.com](mailto:security@fleetdm.com)\n* Join #fleet in [osquery Slack](https://join.slack.com/t/osquery/shared_invite/zt-h29zm0gk-s2DBtGUTW4CFel0f0IjTEw)","published":"2020-12-17T20:15:13.760Z","modified":"2026-07-09T01:30:54.369749Z","cvss":{"score":9.8,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"},"epss":{"score":0.02195,"percentile":0.81621,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/fleetdm/fleet/v4","fixedVersion":"3.5.1"}],"fix":{"url":"https://github.com/fleetdm/fleet/commit/57812a532e5f749c8e18c6f6a652eca65c083607","label":"fleetdm/fleet@57812a5"},"references":[{"type":"ADVISORY","url":"https://github.com/fleetdm/fleet/blob/master/CHANGELOG.md#fleet-351-dec-14-2020"},{"type":"ADVISORY","url":"https://github.com/fleetdm/fleet/security/advisories/GHSA-w3wf-cfx3-6gcx"},{"type":"ADVISORY","url":"https://github.com/mattermost/xml-roundtrip-validator"},{"type":"ADVISORY","url":"https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities"},{"type":"FIX","url":"https://github.com/fleetdm/fleet/commit/57812a532e5f749c8e18c6f6a652eca65c083607"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2020-26276"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-09T01:30:54.369749Z"}}