Fortinet Multiple Products Heap-based Buffer Overflow Vulnerability

What it is

Fortinet FortiOS, FortiSwitchManager, and FortiSASE contain a heap-based buffer overflow vulnerability that allows an attacker to execute unauthorized code or commands via specially crafted packets.

VulnCheck tracked exploitation 1 day before CISA's KEV listing. VulnCheck's broader catalog of in-the-wild exploitation evidence picked this up before it landed on CISA's formal list. Per-CVE fact about this entry; not a population claim about lead time in general.

Who's affected

Affects anyone whose internet connection goes through a Fortinet appliance — typically a FortiGate firewall or FortiClient VPN. The firewall sits between every device in the office and the internet; exploitation can mean an attacker gets inside the network perimeter without touching a workstation.

What to do

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

If you don't have someone in-house to verify the patch deployed across every endpoint — or you're not sure whether you're affected — that's exactly the kind of triage we do. Book a free 20-minute triage call.

CISA due date

Federal deadline: September 12, 2026. Federal agencies must complete the required action by this date. For private SMBs the deadline is advisory — but treat it as a strong recommendation, especially if you handle regulated data (HIPAA, GLBA, ABA model rules).

EPSS

EPSS score: 0.8% — higher than 53% of all scored CVEs.

EPSS estimates the probability of exploitation activity in the next 30 days. Every entry on this site is already confirmed exploited, so read it as relative urgency among the things you still have open, not as permission to wait.

Score dated 2026-09-09, from the FIRST.org Exploit Prediction Scoring System.

Other exploited Fortinet Multiple Products entries

More CISA KEV entries for Fortinet Multiple Products. Same product line, same actively-exploited status.

• CVE-2026-24858: Fortinet Multiple Products Authentication Bypass Using an Alternate Path or Channel Vulnerability
• CVE-2025-59718: Fortinet Multiple Products Improper Verification of Cryptographic Signature Vulnerability
• CVE-2025-32756: Fortinet Multiple Products Stack-Based Buffer Overflow Vulnerability
• CVE-2024-23113: Fortinet Multiple Products Format String Vulnerability
• CVE-2022-40684: Fortinet Multiple Products Authentication Bypass Vulnerability

Browse more

• All Fortinet KEV entries
• Firewalls & edge
• All SMB-relevant KEV entries

Source

This entry comes from CISA's Known Exploited Vulnerabilities catalog, public US-Government data we pull daily. The plain-language framing and the what-to-do guidance above are ours. View the original entry on cisa.gov.