On October 6th, Fortinet sent an advance notice email to selected customers notifying them of CVE-2022-40684, a critical severity vulnerability (CVSS: 9.6) authentication bypass on the administrative interface of FortiOS / FortiProxy.

Affected versions and software include:

  • FortiOS version 7.2.0 through 7.2.1
  • FortiOS version 7.0.0 through 7.0.6
  • FortiProxy version 7.2.0
  • FortiProxy version 7.0.0 through 7.0.6
  • FortiSwitchManager version 7.2.0
  • FortiSwitchManager version 7.0.0

Mitigation steps and workarounds can be found at: https://www.fortiguard.com/psirt/FG-IR-22-377

How to track FortiOS Authentication Bypass Attempt

GreyNoise was contacted by Horizon3 for collaboration of their ongoing research into the FortiOS vulnerability. They graciously provided the necessary information needed to accurately tag this vulnerability.

GreyNoise users can track IPs attempting to exploit CVE-2022-40684 via:

Users can also search for the vulnerabilities using GNQL by CVE –

<span class="code-block" fs-test-element="rich-text">cve:CVE-2022-40684</span>

or by tag name –

<span class="code-block" fs-test-element="rich-text">tags:”FortiOS Authentication Bypass Attempt”</span>

What we know

As of October 13, GreyNoise has observed IPs attempting internet-wide exploitation of this vulnerability, with activity increasing quickly over the past 24 hours. We are aware of several Proof-Of-Concept (POC) code examples to exploit CVE-2022-40684 and expect related exploitative network activity to continue to increase now that these are publicly available.

FortiOS handles API calls by proxying all requests to an interface that is only accessible internally. This internal interface is responsible for verifying authentication and authorization. Proxied requests contain some additional parameters which can be used by FortiOS to bypass or authenticate internal requests. This allows an attacker to masquerade as an internal system API call, bypassing authentication on all externally-facing API endpoints.

Horizon3 has demonstrated leveraging the exploit to achieve authenticated SSH access to vulnerable devices as well as a blog on relevant Indicators Of Compromise (IOCs):

Independent of any knowledge of Horizon3’s collaboration with GreyNoise, one of our engineers (Ian Ling) got curious and spent some time over the weekend researching the vulnerability, leading to successful exploitation with a slightly different methodology.

Authentication bypass in FortiOS / FortiProxy (CVE-2022-40684) is trivial to exploit and users should patch or employ mitigations immediately.

Recommended next steps

If you need to buy time under SLAs: use a block list and apply mitigations, check for presence of IOCs, and work towards upgrading software.

This article is a summary of the full, in-depth version on the GreyNoise Labs blog.
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