CVE-2025-15350

Executive Summary

CVE-2025-15350 is a critical deserialization vulnerability in Anritsu VectorStar, a high-performance vector network analyzer (VNA) used in RF and microwave testing. The flaw resides in the parsing of CHX files, where untrusted data is deserialized without proper validation. An attacker can exploit this by convincing a user to open a malicious CHX file or visit a crafted web page, leading to remote code execution (RCE) in the context of the current process. The vulnerability has a CVSS score of 7.8 (High) and is currently unpatched. No public exploit code or proof-of-concept is available, but the risk is significant due to the potential for full system compromise in critical test and measurement environments.

This vulnerability is not related to any open-source package (NPM, PyPI, Go, Ruby) and does not involve a WordPress plugin. It is a proprietary desktop application vulnerability.

CVSS Breakdown & Threat Level

• CVSS Score: 7.8 (High)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
• 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 a 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 complete compromise of the VectorStar application and potentially the underlying system. In a lab or production environment, this could lead to data theft, configuration manipulation, or lateral movement.

Deep Dive & Mechanics

The vulnerability is a classic deserialization of untrusted data (CWE-502). The Anritsu VectorStar application parses CHX files, which are likely configuration or measurement data files. The parsing routine does not properly validate the serialized objects within the CHX file, allowing an attacker to inject malicious serialized data.

When the application deserializes this data, it can instantiate arbitrary objects, leading to code execution. The specific flaw is in the handling of the CHX file format, which may use Java serialization, .NET binary serialization, or a custom serialization protocol. The attacker can craft a CHX file that, when opened, triggers the deserialization of a gadget chain that executes shellcode or spawns a reverse shell.

The vulnerability is triggered by user interaction (opening a file or visiting a malicious page), but in a targeted attack, social engineering (e.g., "Open this calibration file") is sufficient.

Vulnerable vs. Patched Code

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

# Pseudo-code of vulnerable deserialization
def parse_chx(file_path):
    with open(file_path, 'rb') as f:
        data = f.read()
    # Vulnerable: no validation before deserialization
    obj = deserialize(data)  # e.g., pickle.loads(data) or similar
    process_object(obj)

A patched version would include validation:

# Pseudo-code of patched deserialization
def parse_chx(file_path):
    with open(file_path, 'rb') as f:
        data = f.read()
    # Validate data structure before deserialization
    if not is_valid_chx_format(data):
        raise ValueError("Invalid CHX file")
    # Use a safe deserialization method or allowlist
    obj = safe_deserialize(data, allowed_classes=['Measurement', 'Config'])
    process_object(obj)

The patch would involve implementing input validation, using a deny list or allow list for deserializable classes, or switching to a safer data format like JSON with schema validation.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Anritsu VectorStar installed on a target machine.
• Ability to deliver a malicious CHX file (e.g., via email, USB, or web download).

Exploitation Steps:

1. Craft Malicious CHX File: Use a deserialization tool (e.g., ysoserial for Java, or a custom script for .NET) to generate a payload that executes a reverse shell or drops a backdoor.
2. Deliver Payload: Send the malicious CHX file to the victim via phishing email or host it on a malicious website.
3. Trigger Execution: The victim opens the CHX file in VectorStar, triggering the deserialization and executing the payload.

Example Payload Generation (Java deserialization):

java -jar ysoserial.jar CommonsCollections1 'calc.exe' > malicious.chx

Note: The exact gadget chain depends on the libraries used by VectorStar. If VectorStar uses .NET, tools like ysoserial.net can be used.

Blue Team (Defense & Detection)

Defensive Measures:

• User Awareness: Train users not to open CHX files from untrusted sources.
• File Validation: Implement a pre-processor that validates CHX files before they reach VectorStar.
• Application Sandboxing: Run VectorStar in a sandboxed environment (e.g., using AppContainer or Docker) to limit the impact of exploitation.
• Endpoint Detection: Monitor for unusual child processes spawned by VectorStar (e.g., cmd.exe, powershell.exe).

Detection Rules:

• Monitor for file writes to temporary directories by VectorStar.
• Alert on network connections initiated by VectorStar to unknown IPs.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (Placeholder – no known samples)
  • e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 (example)
• Network Indicators:
  • Outbound connections from VectorStar process to unusual IPs/ports.
  • DNS queries for known C2 domains.
• Process Indicators:
  • VectorStar spawning cmd.exe, powershell.exe, or wscript.exe.
  • Unusual child processes (e.g., rundll32.exe, regsvr32.exe).
• File Indicators:
  • CHX files with unusually large size or containing serialized object headers (e.g., \xac\xed\x00\x05 for Java, or \x00\x01\x00\x00\x00\xff\xff\xff\xff for .NET).

Detection Engineering

YARA Rule

rule CVE_2025_15350_Anritsu_CHX_Deserialization {
    meta:
        description = "Detects malicious CHX files exploiting CVE-2025-15350"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-15350"
    strings:
        $java_serial = { AC ED 00 05 }  // Java serialization magic bytes
        $dotnet_serial = { 00 01 00 00 00 FF FF FF FF }  // .NET serialization header
        $chx_magic = "CHX" nocase
    condition:
        $chx_magic at 0 and ($java_serial or $dotnet_serial)
}

Sigma Rule

title: Anritsu VectorStar CHX Deserialization Exploitation
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects exploitation attempts of CVE-2025-15350 via process anomalies
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        ParentImage|endswith: 'VectorStar.exe'
        Image|endswith:
            - 'cmd.exe'
            - 'powershell.exe'
            - 'wscript.exe'
            - 'cscript.exe'
    condition: selection
falsepositives:
    - Legitimate administrative tasks
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"CVE-2025-15350 Anritsu VectorStar CHX Deserialization - Potential C2"; flow:to_server,established; content:"CHX"; nocase; pcre:"/^.{0,100}CHX/smi"; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate VectorStar: If possible, run VectorStar on an air-gapped machine or in a sandboxed environment.
2. User Training: Educate users about the risks of opening CHX files from untrusted sources.
3. File Filtering: Implement email and web gateway rules to block CHX files.

Long-Term Fix:

• Vendor Patch: Await an official patch from Anritsu. Contact Anritsu support for updates.
• Workaround: If source code is available, implement input validation and safe deserialization as described in the "Vulnerable vs. Patched Code" section.
• Alternative: Consider using a different VNA software or converting CHX files to a safer format (e.g., CSV) before processing.

Monitoring:

• Deploy the YARA, Sigma, and Suricata rules provided above.
• Enable detailed logging for VectorStar processes and file access.

Valters IT