Introduction
Attackers can gain unauthorized code execution on Fortinet FortiOS appliances by sending specially crafted packets. That puts critical network infrastructure at risk. The flaw affects a broad range of FortiOS versions, so it matters to any enterprise running a mix of FortiGate deployments.
Fortinet makes a wide range of network security products and is best known for its FortiGate firewalls and the FortiOS operating system. Its technology is deployed in enterprises, service providers, and government agencies worldwide.
Technical Information
CVE-2025-53843 is a stack-based buffer overflow in Fortinet FortiOS, triggered when a vulnerable device receives specially crafted packets. It is classified as CWE-121 and comes from improper memory handling on the stack. When a stack-allocated buffer is overrun, the overflow can overwrite adjacent memory, including function return addresses. That can let an attacker execute arbitrary code or commands on the device.
The bug spans multiple major and minor versions of FortiOS, which suggests the root cause sits in shared or long-standing code. The exact protocol or packet structure needed to exploit it has not been made public, and no vulnerable code snippets or proof of concept have been released.
Affected Systems and Versions
- FortiOS 7.6.0 through 7.6.3
- FortiOS 7.4.0 through 7.4.8
- FortiOS 7.2 (all versions)
- FortiOS 7.0 (all versions)
- FortiOS 6.4 (all versions)
No specific configuration requirements or exclusions are documented in public sources.
Vendor Security History
Fortinet has a documented history of buffer overflow and memory corruption vulnerabilities in FortiOS and related products. Previous advisories have covered similar stack-based and heap-based issues, and those issues have often hit several version branches at once. Fortinet generally releases patches promptly, though some advisories have drawn criticism for delayed public disclosure. The company works regularly with the security research community and maintains an active PSIRT.
