How do you patch or mitigate CVE-2024-23113 (Fortinet Multiple Products Format String)?

CISA’s required action for CVE-2024-23113 is to apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable. In practice, find every instance of Fortinet Multiple Products in your estate, apply the vendor security update or documented mitigation, and if no fix can be applied, remove internet exposure or take the product out of service.

What this CVE means operationally

CVE-2024-23113 is not something to manage with a generic “patch later” mindset. The practical question is whether any Fortinet Multiple Products instance is still reachable, still supported, and still able to receive the vendor’s security update or mitigation. If the answer is no, the remediation choice shifts from patching to exposure reduction or retirement.

That distinction matters because format string flaws can be exploited in ways that are hard to notice until after initial compromise. For internet-facing appliances, the most important first step is confirming every deployment, not just the obvious production systems, including lab, failover, and edge units that may have been forgotten during asset tracking.

For confirmation and version details, use the vendor advisory and the CISA Known Exploited Vulnerabilities Catalog rather than relying on memory or secondary summaries.

How to apply the fix or mitigation

The remediation path is straightforward in principle: apply the vendor security update or the documented mitigation exactly as published by Fortinet. If a direct fix is available, treat it as the preferred option because it removes the condition rather than compensating for it. If you cannot patch immediately, the mitigation must materially reduce exposure, not merely document the risk.

For appliances that cannot be updated promptly, isolate them from public access, remove unnecessary management exposure, and narrow the reachable attack surface as much as possible. If mitigations are unavailable or cannot be verified, CISA’s required action is to discontinue use of the product, which in practice means taking it out of service or replacing it.

Use the NIST National Vulnerability Database and the CVE Program to confirm the record, then validate the vendor’s fix instructions against the exact product family in your estate.

What to verify before you call it resolved

Resolution should be verified, not assumed. Confirm that the affected product is no longer exposed on the internet, that the vendor update or mitigation was applied to every instance, and that no alternate interface, standby node, or clustered peer still presents the same attack surface. If the appliance is part of a larger perimeter stack, check both the external service and any administrative paths.

Where patching was delayed, review logs and alerts for signs of prior exploitation before declaring closure. An exploited edge product can become a foothold for credential theft, configuration tampering, or lateral movement, so the remediation record should include the date exposure ended, the control applied, and the evidence used to verify success.

NHIMG’s Edge Device Security Guide is useful here because it focuses on management exposure, patching, logging minimums, and end-of-life planning for internet-facing appliances.

Risk and Threat Considerations

Format string flaws on perimeter appliances are high-consequence because they can expose code execution or memory corruption paths on systems that sit directly on the trust boundary. If the device is internet-facing, the risk is not just the vulnerability itself, but the speed with which an attacker can turn it into durable access or follow-on compromise.

Failure mechanism: The flaw can be triggered through crafted input that reaches a vulnerable parsing path, allowing an attacker to influence memory handling or program flow. If the device cannot be updated, the remaining exposure is the reachable service, so mitigation quality depends on whether the attack surface is actually removed or merely reduced.

Impact: Successful exploitation of an edge appliance can lead to device takeover, traffic interception, credential exposure, or pivoting into adjacent systems. Where the product remains in service without a verified fix, the residual risk is continued exploitable exposure rather than a one-time defect.

Standards & Framework Alignment

This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.

CIS Controls v8 and NIST SP 800-53 Rev 5 set the technical controls, while ISO/IEC 27001:2022 defines the regulatory obligations.

Framework	Control / Reference	Relevance
CIS Controls v8	CIS-7 — Continuous Vulnerability Management	The page is about remediating an exploited CVE through patching or mitigation.
Recommendation — Prioritise, patch, and verify remediation for KEV-listed exposures before attackers exploit them.
NIST SP 800-53 Rev 5	SI-2 — Flaw Remediation	This CVE response is fundamentally about applying vendor fixes or compensating mitigations.
	RA-5 — Vulnerability Monitoring and Scanning	You must find every Fortinet instance and confirm exposure before and after remediation.
Recommendation — Apply vendor fixes or compensating measures and verify remediation across all affected assets. Scan for all exposed instances and validate that remediation eliminated the vulnerable condition.
ISO/IEC 27001:2022	A.8.8 — Management of technical vulnerabilities	The subject requires handling a published vulnerability through controlled remediation.
	A.8.9 — Configuration management	Mitigation may require reducing internet exposure and changing appliance configuration.
Recommendation — Track and remediate the vulnerability under a formal technical vulnerability management process. Harden or reconfigure the appliance to remove unnecessary exposure while remediation is pending.

Practitioner Guidance

What to prioritise: Inventory every Fortinet Multiple Products deployment first, then sort them by internet exposure and operational criticality. Public-facing or management-reachable instances should move to the front of the queue because they carry the highest exploitation risk.

Decision rule: If the vendor update can be applied safely, patch and verify immediately; if it cannot, apply the documented mitigation and remove public reachability. If neither is possible, decommission the product rather than carrying open exposure.

What to verify: Keep proof of the exact software state before and after remediation, plus evidence that management interfaces and external services are no longer exposed where they should not be. That evidence is what separates a completed fix from an assumed one.

Practitioner takeaway: With KEV-listed edge-device flaws, speed matters, but verified exposure removal matters more when patching is delayed or impossible.