CVE-2020-26276

Name: CVE-2020-26276
Creator: NVD / NIST
Published: 2020-12-17T20:15:13.76+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 2.17%

Last modified Jun 17, 2026

CVE-2020-26276 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. 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. EPSS estimates a 2.17% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

2.17%

80.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Fleetdm	Fleet	< 3.5.1

References

https://github.com/fleetdm/fleet/blob/master/CHANGELOG.md#fleet-351-dec-14-2020Release Notes, Third Party Advisory
https://github.com/fleetdm/fleet/commit/57812a532e5f749c8e18c6f6a652eca65c083607Patch, Third Party Advisory
https://github.com/fleetdm/fleet/security/advisories/GHSA-w3wf-cfx3-6gcxThird Party Advisory
https://github.com/mattermost/xml-roundtrip-validatorThird Party Advisory
https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilitiesNot Applicable, Third Party Advisory
https://github.com/fleetdm/fleet/blob/master/CHANGELOG.md#fleet-351-dec-14-2020Release Notes, Third Party Advisory
https://github.com/fleetdm/fleet/commit/57812a532e5f749c8e18c6f6a652eca65c083607Patch, Third Party Advisory
https://github.com/fleetdm/fleet/security/advisories/GHSA-w3wf-cfx3-6gcxThird Party Advisory
https://github.com/mattermost/xml-roundtrip-validatorThird Party Advisory
https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilitiesNot Applicable, Third Party Advisory

Timeline

Published: Dec 17, 2020
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2020-26276?

How severe is CVE-2020-26276?

CVE-2020-26276 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 2.17% probability of exploitation in the next 30 days.

How do I fix CVE-2020-26276?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2020-26276?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST