Fleet, SAML Authentication Bypass, CVE-2023-XXXX (Critical)

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How the CVE Works:

The vulnerability in Fleet arises due to improper validation of SAML responses. An attacker can craft a malicious SAML response with forged assertions, exploiting the lack of proper signature verification. When Just-In-Time (JIT) provisioning is enabled, the attacker can create a new administrative user account. Additionally, if MDM enrollment is enabled, certain endpoints can be abused to create accounts tied to these forged assertions. This allows unauthorized access to Fleet, including administrative privileges, device data visibility, and configuration modification. The issue is rooted in the SAML authentication process, where the application fails to validate the integrity and authenticity of the SAML response, leading to authentication bypass.

DailyCVE Form:

Platform: Fleet
Version: < 4.64.2
Vulnerability: SAML Authentication Bypass
Severity: Critical
Date: YYYY-MM-DD

(End of form)

What Undercode Say:

Analytics:

  • Exploitation Likelihood: High due to the ease of crafting malicious SAML responses.
  • Attack Vector: Remote exploitation via SAML response manipulation.
  • Impact Scope: Full administrative access, device data exposure, and configuration changes.

Commands:

1. Check Fleet Version:

fleetctl version

2. Disable SSO Temporarily:

fleetctl config set --sso.enabled=false

3. Upgrade Fleet:

fleetctl upgrade --version 4.64.2

Exploitation Details:

  • Crafting Malicious SAML Response:
    Use tools like `SAML-tracer` or `Burp Suite` to manipulate SAML assertions.

Example SAML response modification:

<saml:Assertion ...>
<saml:AttributeStatement>
<saml:Attribute Name="Role">Admin</saml:Attribute>
</saml:AttributeStatement>
</saml:Assertion>

Protection Measures:

  1. Apply Patch: Upgrade to Fleet version 4.64.2 or later.
  2. Validate SAML Signatures: Ensure SAML responses are properly signed and validated.
  3. Disable JIT Provisioning: Temporarily disable JIT if not required.
  4. Monitor Logs: Use Fleet’s logging to detect unusual authentication attempts.

References:

Code Snippets:

  • Python Script to Validate SAML Response: 
    from onelogin.saml2.response import OneLogin_Saml2_Response
saml_response = OneLogin_Saml2_Response(settings, request_data)
if saml_response.is_valid():
print("SAML Response is valid.")
else:
print("SAML Response is invalid.")
  • Log Monitoring Command: 
    fleetctl logs --filter="authentication"

    By following these steps, users can mitigate the risk of exploitation and secure their Fleet instances effectively.

References:

Reported By: https://github.com/advisories/GHSA-52jx-g6m5-h735
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