CVE-2025-2449

Executive Summary

CVE-2025-2449 is a high-severity directory traversal vulnerability in NI FlexLogger, specifically within the usiReg component’s parsing of URI files. The flaw allows remote attackers to create arbitrary files on the target system by tricking a user into visiting a malicious page or opening a malicious file. The vulnerability stems from improper validation of user-supplied paths before file operations, enabling code execution in the context of the current user. With a CVSS score of 7.8, this vulnerability poses a significant risk to industrial control and data acquisition environments where FlexLogger is deployed. No public exploit code or patch is currently available, but the risk is elevated due to the potential for lateral movement and data exfiltration.

CVSS Breakdown & Threat Level

• CVSS Score: 7.8 (High)
• Attack Vector: Local (AV:L) – requires user interaction
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: Required (UI:R)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: High (I:H)
• Availability Impact: High (A:H)
• Threat Level: High – exploitation can lead to arbitrary file creation and code execution, potentially compromising the entire system.

Deep Dive & Mechanics

The vulnerability resides in the usiReg component of NI FlexLogger, which processes URI files. The core issue is a classic directory traversal (CWE-22) where the application fails to sanitize user-supplied paths. When a user opens a malicious URI file (e.g., via a crafted .url or .lnk file), the usiReg component interprets the path without proper validation, allowing an attacker to write files to arbitrary locations on the filesystem.

Attack Flow:

1. An attacker crafts a malicious URI file containing a path traversal sequence (e.g., ../../Windows/System32/malicious.dll).
2. The attacker hosts this file on a website or sends it via email.
3. The victim, using NI FlexLogger, opens the malicious file.
4. The usiReg component parses the URI and writes the attacker-controlled content to the traversed path.
5. This can lead to arbitrary code execution if the written file is a DLL, executable, or script that gets loaded or executed.

The vulnerability is particularly dangerous because it does not require authentication or elevated privileges—only user interaction. In industrial environments, FlexLogger is often used for data acquisition, and a compromised system could lead to operational disruption or data theft.

Vulnerable vs. Patched Code

Since no official patch is available, the vulnerable code pattern is inferred from the CVE description. The usiReg component likely uses a function similar to the following:

Vulnerable Code (C++/C# pseudo):

void ParseURI(const string& uriPath) {
    string fullPath = "C:\\ProgramData\\NI\\FlexLogger\\" + uriPath;
    // No validation of path traversal
    WriteFile(fullPath, data);
}

Patched Code (hypothetical):

void ParseURI(const string& uriPath) {
    string sanitizedPath = SanitizePath(uriPath);
    if (!IsWithinAllowedDirectory(sanitizedPath)) {
        throw SecurityException("Invalid path");
    }
    string fullPath = "C:\\ProgramData\\NI\\FlexLogger\\" + sanitizedPath;
    WriteFile(fullPath, data);
}

The patched version would validate that the resolved path stays within an allowed directory, preventing traversal.

Exploitation & Lab Setup

Red Team

Lab Environment:

• Windows 10/11 with NI FlexLogger installed (any version).
• Attacker machine with a web server or email client.

Exploitation Steps:

1. Create a malicious URI file (e.g., exploit.url) with the following content:

   [InternetShortcut]
   URL=file:///C:/Users/Public/malicious.dll
   WorkingDirectory=C:\Windows\System32
   

   However, the traversal is triggered via the usiReg component. A more precise payload would be:

   [InternetShortcut]
   URL=usiReg://../../Windows/System32/malicious.dll
   

2. Host the file on a web server or send it as an email attachment.
3. Convince the target user to open the file.
4. The usiReg component writes the attacker-controlled DLL to C:\Windows\System32\malicious.dll.
5. Execute the DLL via a scheduled task or other means (e.g., rundll32.exe C:\Windows\System32\malicious.dll,EntryPoint).

Note: No public exploit code is available, so this is a conceptual demonstration.

Blue Team

Detection:

• Monitor for unusual file writes to system directories (e.g., C:\Windows\System32, C:\Program Files).
• Alert on processes (e.g., FlexLogger.exe) writing files outside their expected data directories.
• Use Sysmon to log file creation events (Event ID 11) and correlate with process creation.

Prevention:

• Restrict user permissions to prevent writes to sensitive directories.
• Enable AppLocker or Windows Defender Application Control to block unauthorized executables.
• Use endpoint detection and response (EDR) tools to block suspicious file writes.

Indicators of Compromise (IOCs)

• File Hashes (example, not actual):
  • malicious.dll: SHA256 a1b2c3d4e5f6...
• File Paths:
  • C:\Windows\System32\malicious.dll
  • C:\Users\<username>\AppData\Local\Temp\*.dll
• Process Names:
  • FlexLogger.exe
  • usiReg.exe (if separate)
• Network Indicators:
  • Connections to known malicious IPs or domains hosting the URI file.
• Registry Keys (if persistence is achieved):
  • HKCU\Software\Microsoft\Windows\CurrentVersion\Run\Malicious

Detection Engineering

YARA Rule

rule CVE_2025_2449_Malicious_URI {
    meta:
        description = "Detects malicious URI files exploiting CVE-2025-2449"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-2449"
    strings:
        $s1 = "usiReg://" nocase
        $s2 = "../" nocase
        $s3 = "..\\" nocase
        $s4 = "Windows\\System32" nocase
    condition:
        any of ($s*) and filesize < 10KB
}

Sigma Rule

title: CVE-2025-2449 - NI FlexLogger Directory Traversal
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects file writes by FlexLogger to suspicious directories
author: Valters IT
date: 2025-04-10
logsource:
    category: file_event
    product: windows
detection:
    selection:
        Image|endswith: '\FlexLogger.exe'
        TargetFilename|contains:
            - '\Windows\System32\'
            - '\Windows\SysWOW64\'
            - '\Program Files\'
    condition: selection
falsepositives:
    - Legitimate updates or configuration changes
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-2449 - Malicious URI File Download"; flow:to_client; file.name; content:".url"; nocase; file.name; content:"usiReg"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected systems: Disconnect NI FlexLogger from untrusted networks.
2. User awareness: Train users not to open unsolicited URI files or links.
3. Restrict file types: Block .url, .lnk, and .website files via email and web gateways.

Long-term Fix:

• Monitor NI’s advisory page for an official patch. Until then, consider using a third-party security tool to sandbox FlexLogger.
• Implement application whitelisting to prevent unauthorized executables.
• Use a host-based intrusion prevention system (HIPS) to block directory traversal attempts.

Workaround:

• Modify the usiReg component’s configuration to restrict write paths (if possible).
• Use Windows Defender Exploit Guard to control folder access.

Valters IT