Critical Look: CVE-2025-46776 – FortiExtender CLI Buffer Overflow Puts Networks at Risk

Overview

CVE-2025-46776 is a medium-severity vulnerability affecting Fortinet FortiExtender devices. This vulnerability, classified as a classic buffer overflow, arises from insufficient input validation when processing CLI commands. An authenticated attacker could exploit this flaw to execute arbitrary code or commands on the affected system. This article provides a detailed analysis of the vulnerability, its potential impact, and necessary mitigation steps.

Technical Details

The vulnerability resides in how FortiExtender handles CLI commands. Specifically, a buffer copy operation fails to adequately check the size of the input data. This allows an attacker, authenticated to the FortiExtender device, to craft malicious CLI commands that exceed the buffer’s capacity. By overflowing the buffer, the attacker can overwrite adjacent memory regions, potentially gaining control of the system’s execution flow and executing arbitrary code.

Affected Versions:

• FortiExtender 7.6.0 through 7.6.1
• FortiExtender 7.4.0 through 7.4.6
• FortiExtender 7.2 all versions
• FortiExtender 7.0 all versions

CVSS Analysis

The Common Vulnerability Scoring System (CVSS) assigns CVE-2025-46776 a score of 6.4, indicating a MEDIUM severity.

• CVSS Score: 6.4

While the vulnerability requires authentication, the potential for arbitrary code execution elevates the risk. The CVSS score reflects a balance between the required authentication and the potential impact of a successful exploit.

Possible Impact

A successful exploitation of CVE-2025-46776 could lead to several critical consequences:

• Arbitrary Code Execution: An attacker could execute arbitrary code on the affected FortiExtender device, potentially gaining complete control over the system.
• Command Execution: The attacker could execute arbitrary commands, allowing them to modify configurations, access sensitive data, or disrupt network services.
• Data Breach: Compromised FortiExtender devices could be used as a pivot point to access other systems on the network, leading to a data breach.
• Denial of Service (DoS): An attacker could crash the FortiExtender device, causing a denial of service for connected users.

Mitigation and Patch Steps

The primary mitigation strategy is to update your FortiExtender devices to a patched version that addresses the vulnerability. Fortinet has released fixes to address this issue. Please follow these steps:

1. Identify Affected Devices: Determine which FortiExtender devices in your network are running the vulnerable versions (7.6.0 through 7.6.1, 7.4.0 through 7.4.6, 7.2 all versions, 7.0 all versions).
2. Apply the Patch: Download and install the latest firmware updates from the Fortinet support portal. Refer to the Fortinet advisory FG-IR-25-251 for specific version information and update instructions.
3. Restrict Access: Limit access to the FortiExtender CLI to only authorized personnel.
4. Monitor Logs: Regularly monitor FortiExtender logs for suspicious activity that might indicate an attempted exploit.

References

Fortinet Advisory FG-IR-25-251