CVE-2025-53843: 
FortiOS vulnerability analysis and mitigation

CVE-2025-53843 is a stack-based buffer overflow vulnerability discovered in the CAPWAP daemon of FortiOS and FortiSwitchManager. The vulnerability was initially disclosed on November 18, 2025, affecting multiple versions of FortiOS ranging from 6.4 through 7.6.3. This security flaw has been assigned a medium severity rating with a CVSSv3 score of 6.9 (Fortiguard PSIRT).

The vulnerability is classified as a stack-based overflow vulnerability (CWE-124) in the CAPWAP (Control And Provisioning of Wireless Access Points) daemon. The flaw requires a remote authenticated attacker to send specially crafted packets to potentially execute arbitrary code or commands as a low privileged user. Successful exploitation is complicated by existing security measures, including stack protection and Address Space Layout Randomization (ASLR) (Fortiguard PSIRT).

If successfully exploited, this vulnerability could allow an attacker to execute unauthorized code or commands with low-level privileges on the affected system. However, the impact is somewhat mitigated by the requirement that the attacker must be able to pose as an authorized FortiAP or FortiExtender device (Fortiguard PSIRT, CIS Advisory).

Fortinet has released patches to address this vulnerability. Users are advised to upgrade to FortiOS version 7.6.4 or above for the 7.6 branch, or 7.4.9 or above for the 7.4 branch. For all other affected versions (7.2, 7.0, and 6.4), users should migrate to a fixed release. Fortinet provides an upgrade path tool at their documentation site to assist with the update process (Fortiguard PSIRT).