CVE-2025-25256: Critical Command Injection in Fortinet’s FortiSIEM

CVE-2025-25256 represents a critical pre-authentication command injection vulnerability in Fortinet’s FortiSIEM platform that enables unauthenticated remote code execution with root privileges. This vulnerability affects the phMonitor service running on port 7900 and impacts a wide range of FortiSIEM versions from 5.4 through 7.3.1.

The vulnerability stems from insufficient input validation in the ShellCmd::addParaSafe function, which only performs rudimentary quote escaping, allowing sophisticated injection techniques to bypass security controls.

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Vulnerability Details

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Root Cause Analysis

The vulnerability originates in the phMonitorProcess::handleStorageArchiveRequest function within the phMonitor service. The critical flaw lies in inadequate input sanitization performed by the ShellCmd::addParaSafe function, which implements only basic quote escaping mechanisms insufficient to prevent modern command injection techniques.

Vulnerable Code Flow

• Input Reception: XML payload received on port 7900 via TLS connection
• XML Processing: phBaseXmlParser parses the malicious XML structure
• Parameter Extraction: User-controlled data extracted from XML elements
• Insufficient Sanitization: ShellCmd::addParaSafe performs inadequate input validation
• Command Construction: Shell command built with unsanitized user input
• Command Execution: phMiscUtils::do_system_cancellable executes the compromised command

Attack Vector Diagram

The critical flaw lies in the ShellCmd::addParaSafe function, which was supposed to safely sanitize user inputs but only performed rudimentary quote escaping where a defense that crumbles against modern injection techniques.

Affected Product Versions

The vulnerability affects a broad range of FortiSIEM releases, requiring immediate attention from organizations running affected versions:

Critical Advisory: Organizations running FortiSIEM 6.6.x and earlier versions must migrate to a supported release as no security patches will be provided for these legacy versions.

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Exploitation Methodology

Prerequisites for Successful Exploitation

• Network Access: Direct connectivity to FortiSIEM on port 7900/TCP
• System Configuration: Target system must be operating in Supervisor or Worker mode
• Payload Delivery: Ability to craft and transmit malicious XML payloads via TLS

Attack Execution Process

The exploitation process involves establishing a TLS connection to the phMonitor service and transmitting specially crafted XML payloads containing command injection sequences within the archive_nfs_archive_dir or archive_nfs_server_ip parameters.

Malicious Payload Structure

Command Construction: The vulnerable code constructs the following shell command:

Note: The ${IFS} (Internal Field Separator) technique bypasses space-filtering mechanisms by substituting the IFS environment variable for space characters.

Before the Fix: The Vulnerable Implementation

After the Fix: Proper Validation
Fortinet’s fix demonstrates how input validation should be done:

Security Improvement Analysis:

• Pattern Validation: Implements strict regex patterns for hostnames and IP addresses
• Input Rejection: Throws exceptions for non-conforming input instead of attempting sanitization
• Defense in Depth: Multiple validation layers prevent bypass attempts

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Proof of Concept Exploit

Step 1: Malicious XML Payload Construction

Step 2: Command Execution Analysis

Intended Command:

Actual Executed Command:

Complete Exploit Implementation

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Business Impact Assessment

Security Infrastructure Compromise

When a SIEM system falls to attackers, the consequences cascade through every layer of enterprise security architecture:

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Impact Analysis

1. Complete Platform Compromise

• Root-level system access without authentication barriers
• Lateral movement capabilities via stored credentials and service accounts
• Persistent access establishment through SSH key injection and service modifications

2. Security Monitoring Neutralization

• Detection rule manipulation to disable specific security alerts
• Log integrity compromise making forensic analysis unreliable
• False positive injection to create alert fatigue and mask malicious activity

3. Regulatory and Compliance Exposure

• SOX/PCI/GDPR/HIPAA controls invalidated due to compromised monitoring infrastructure
• Mandatory breach notifications triggered with associated legal and financial penalties
• Audit scrutiny escalation requiring extensive remediation documentation

4. Incident Response Degradation

• Evidence contamination compromising legal proceedings and forensic analysis
• Mean Time to Detection (MTTD) inflation from hours to potentially weeks
• Response team blindness due to unreliable security event data

5. Indicators of Compromise (IOCs)

• Unexpected TLS connections to port 7900/TCP from external IP addresses
• Large XML payloads (>1KB) containing backtick characters or command injection syntax
• Rapid connection attempts to port 7900 indicating automated exploitation scanning
• Outbound connections from FortiSIEM systems to suspicious external destinations

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Key Findings and Recommendations

CVE-2025-25256 serves as a sobering reminder that security solutions themselves are high-value targets and can become single points of failure in enterprise security architectures. This vulnerability highlights several critical lessons:

• Apply defense in depth to security tools.
• Update incident plans for tool compromise.
• Assess vendor risks.

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For more information about securing your email infrastructure or assistance with vulnerability management, contact iZOOlogic’s cybersecurity experts

References

1. Fortinet Security Advisory FG-IR-25-152
   https://fortiguard.fortinet.com/psirt/FG-IR-25-152
2. MITRE CVE-2025-25256 Entry
   https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-25256
3. watchTowr Labs Deep Dive Analysis
   Should Security Solutions Be Secure? FortiSIEM CVE-2025-25256
4. The Hacker News Coverage
   Fortinet Warns About FortiSIEM Vulnerability
5. Common Weakness Enumeration – CWE-78
   OS Command Injection
6. NIST Cybersecurity Framework
   Framework for Improving Critical Infrastructure Cybersecurity