CVE-2025-15351

Executive Summary

CVE-2025-15351 is a critical Remote Code Execution (RCE) vulnerability affecting Anritsu VectorStar, a high-performance vector network analyzer platform. The flaw resides in the parsing of CHX files, where deserialization of untrusted data occurs due to insufficient validation. An attacker can exploit this by convincing a user to open a malicious CHX file or visit a crafted web page, leading to arbitrary code execution in the context of the current process. With a CVSS score of 7.8, this vulnerability poses a significant risk to operational technology (OT) environments, particularly in telecommunications and RF testing labs. No public exploit code or patch is currently available, making detection and mitigation critical.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
• Base Score: 7.8 (High)
• Attack Vector (AV): Local (requires user interaction to open a file)
• Attack Complexity (AC): Low
• Privileges Required (PR): None
• User Interaction (UI): Required (victim must open malicious file)
• Scope (S): Unchanged
• Confidentiality (C): High
• Integrity (I): High
• Availability (A): High

Threat Level: High. Although user interaction is required, the impact is severe, allowing full system compromise. The lack of a patch increases the urgency for detection and mitigation.

Deep Dive & Mechanics

The vulnerability is a classic deserialization of untrusted data (CWE-502) within the CHX file parser of Anritsu VectorStar. CHX files are used to store calibration and measurement data. The parser fails to validate serialized objects before deserializing them, allowing an attacker to craft a malicious CHX file containing a serialized object that, when deserialized, executes arbitrary code.

Technical Breakdown:

1. Entry Point: The VectorStar application loads a CHX file via File > Open or programmatically.
2. Parsing Logic: The parser uses a deserialization routine (likely Java or .NET based) that reads serialized objects from the file.
3. Exploitation: An attacker embeds a malicious serialized object (e.g., a gadget chain) that triggers code execution upon deserialization.
4. Execution Context: The code runs with the privileges of the current user, typically an engineer or technician with local administrative rights.

Attack Scenario:

• An attacker sends a phishing email with a malicious CHX file attachment.
• The victim opens the file in VectorStar.
• The deserialization flaw triggers, executing a payload (e.g., reverse shell, ransomware, or data exfiltration).

Vulnerable vs. Patched Code

Since no patch is available, a direct comparison is not possible. However, the vulnerable code likely resembles:

# Vulnerable pseudo-code (Python-like)
import pickle

def load_chx(filepath):
    with open(filepath, 'rb') as f:
        data = f.read()
        # No validation before deserialization
        obj = pickle.loads(data)  # Vulnerable
        process(obj)

A patched version would include input validation and safe deserialization:

# Patched pseudo-code
import pickle
import re

def load_chx(filepath):
    with open(filepath, 'rb') as f:
        data = f.read()
        # Validate file structure before deserialization
        if not is_valid_chx(data):
            raise ValueError("Invalid CHX file")
        # Use a safe deserialization method
        obj = safe_deserialize(data)  # Patched
        process(obj)

def safe_deserialize(data):
    # Implement whitelist-based deserialization
    # or use a sandboxed environment
    pass

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Anritsu VectorStar installed (any version)
• Python 3.x with pickle or yaml for crafting payloads
• A listener for reverse shell (e.g., netcat)

Step-by-Step Exploitation:

1. Craft Malicious CHX File:
   • Use a deserialization gadget chain (e.g., for Python pickle or Java).
   • Example using Python's pickle:

import pickle
import os

class Exploit:
    def __reduce__(self):
        return (os.system, ('calc.exe',))

payload = pickle.dumps(Exploit())
with open('malicious.chx', 'wb') as f:
    f.write(payload)

2. Deliver File:

   • Send via email or host on a malicious website.

3. Trigger Exploit:

   • Victim opens malicious.chx in VectorStar.
   • Code executes (e.g., launches calculator or reverse shell).

Note: No public exploit code exists; this is a conceptual demonstration.

Blue Team (Detection & Defense)

Detection Steps:

1. Monitor File Operations: Alert on CHX file opens by VectorStar process.
2. Network Monitoring: Detect outbound connections from VectorStar hosts.
3. Endpoint Detection: Use EDR to monitor for unusual child processes spawned by VectorStar.

Defense Measures:

• Disable CHX file association or restrict file types.
• Use application whitelisting to prevent VectorStar from executing untrusted code.
• Implement network segmentation for OT devices.

Indicators of Compromise (IOCs)

Detection Engineering

YARA Rule

rule CVE_2025_15351_CHX_Deserialization {
    meta:
        description = "Detects malicious CHX files exploiting CVE-2025-15351"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-15351"
    strings:
        $pickle_magic = { 80 04 95 }  // Python pickle protocol 4 magic bytes
        $java_serial = { AC ED 00 05 }  // Java serialization magic
        $yaml_magic = "!!python/object:"  // YAML deserialization
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-15351 - Anritsu VectorStar CHX Deserialization
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects exploitation attempts of CVE-2025-15351 via CHX file opens
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\VectorStar.exe'
        CommandLine|contains: '.chx'
    condition: selection
falsepositives:
    - Legitimate CHX file opens by authorized users
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-15351 - Anritsu VectorStar CHX Deserialization Outbound"; flow:to_server,established; content:"|80 04 95|"; depth:3; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable CHX File Parsing: If possible, block CHX file types at the perimeter or via group policy.
2. User Awareness: Train users not to open CHX files from untrusted sources.
3. Network Segmentation: Isolate VectorStar hosts from the internet and untrusted networks.

Long-Term Fix:

• Await an official patch from Anritsu. Monitor their security advisories.
• Implement application-level input validation and safe deserialization practices.

Workaround:

• Use a file scanner to detect malicious serialization patterns before opening CHX files.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert