CVE-2025-64157: Fortinet FortiOS RCE Vulnerability

CVE-2025-64157 Overview

CVE-2025-64157 is a use of externally-controlled format string vulnerability affecting Fortinet FortiOS across multiple versions. This vulnerability allows an authenticated administrator to execute unauthorized code or commands through specifically crafted configuration inputs. Format string vulnerabilities occur when user-controlled input is passed directly to formatting functions without proper sanitization, enabling attackers to read or write arbitrary memory locations.

Critical Impact

Authenticated administrators can leverage malicious configuration inputs to achieve arbitrary code execution on affected FortiOS devices, potentially compromising network security infrastructure.

Affected Products

• Fortinet FortiOS 7.6.0 through 7.6.4
• Fortinet FortiOS 7.4.0 through 7.4.9
• Fortinet FortiOS 7.2.0 through 7.2.11
• Fortinet FortiOS 7.0 all versions

Discovery Timeline

• 2026-02-10 - CVE-2025-64157 published to NVD
• 2026-02-12 - Last updated in NVD database

Technical Details for CVE-2025-64157

Vulnerability Analysis

This vulnerability stems from improper handling of format string specifiers in configuration input processing. When an authenticated administrator submits specially crafted configuration data, the system passes user-controlled strings directly to formatting functions (such as printf() family functions) without proper validation. This enables an attacker with administrative privileges to inject format specifiers like %n, %x, or %s that can manipulate program execution flow, read sensitive memory contents, or write to arbitrary memory locations.

The attack requires administrative credentials to access the configuration interface, limiting the initial attack surface. However, in scenarios involving compromised administrator accounts, insider threats, or privilege escalation chains, this vulnerability provides a pathway to execute arbitrary code on the underlying FortiOS system.

Root Cause

The root cause is classified as CWE-134 (Use of Externally-Controlled Format String). The vulnerable code path accepts configuration input from authenticated administrators and processes it through formatting functions without sanitizing or escaping format specifiers. This design flaw allows the format string specifiers embedded in user input to be interpreted as formatting instructions rather than literal string data.

Attack Vector

The attack vector is network-based, requiring the attacker to have authenticated administrator-level access to the FortiOS management interface. The attacker crafts malicious configuration parameters containing format string specifiers and submits them through the administrative interface. The vulnerability does not require user interaction beyond the attacker's own administrative session.

The exploitation chain involves injecting format specifiers into configuration fields that are subsequently processed by vulnerable formatting functions. Using specifiers like %n to write to memory or %x to leak stack contents, an attacker can manipulate program state to achieve code execution. For detailed technical analysis, refer to the Fortinet PSIRT Advisory FG-IR-25-795.

Detection Methods for CVE-2025-64157

Indicators of Compromise

• Unusual configuration changes containing format string specifiers (%n, %x, %s, %p) in configuration fields
• Unexpected administrative session activity or configuration modifications from unknown IP addresses
• System crashes or unexpected behavior following configuration changes
• Log entries showing malformed configuration attempts or memory access violations

Detection Strategies

• Monitor administrative configuration changes for patterns containing format string characters and specifiers
• Implement behavioral analysis on FortiOS management interfaces to detect anomalous configuration submissions
• Review authentication logs for signs of compromised administrator accounts or unusual access patterns
• Deploy network traffic analysis to identify exploitation attempts targeting management interfaces

Monitoring Recommendations

• Enable comprehensive logging for all administrative actions and configuration changes on FortiOS devices
• Configure alerts for configuration modifications containing suspicious character sequences
• Monitor system stability metrics that may indicate memory corruption from exploitation attempts
• Implement session monitoring to track administrative access duration and activity patterns

How to Mitigate CVE-2025-64157

Immediate Actions Required

• Upgrade FortiOS to a patched version as specified in the Fortinet security advisory
• Audit and restrict administrative account access to trusted personnel only
• Review recent configuration changes for signs of exploitation attempts
• Isolate management interfaces from untrusted network segments

Patch Information

Fortinet has released security updates to address this vulnerability. Administrators should consult the Fortinet PSIRT Advisory FG-IR-25-795 for specific patched versions and upgrade instructions. Prioritize patching based on the network criticality of affected FortiOS devices.

Workarounds

• Restrict administrative interface access to trusted IP addresses using access control lists
• Implement multi-factor authentication for all administrative accounts
• Segment management networks to limit exposure of administrative interfaces
• Conduct regular audits of administrator account permissions and remove unnecessary access

# Example: Restrict admin access to trusted management network
config system admin
    edit "admin"
        set trusthost1 10.10.10.0 255.255.255.0
    next
end