CVE-2026-26101

Executive Summary

CVE-2026-26101 is a critical security vulnerability in Owl opds version 2.2.0.4, involving Incorrect Permission Assignment for Critical Resource (CWE-732). The flaw allows an attacker to manipulate files on the target system by sending a crafted network request. This vulnerability can lead to unauthorized file modification, deletion, or corruption, potentially compromising the integrity of the application and underlying system. No patch is currently available, and no public proof-of-concept (PoC) has been released.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating insufficient data for a complete assessment. However, based on the nature of the vulnerability (file manipulation via network request), the likely vector would be:

• Attack Vector (AV): Network (N)
• Attack Complexity (AC): Low (L)
• Privileges Required (PR): None (N)
• User Interaction (UI): None (N)
• Scope (S): Unchanged (U)
• Confidentiality (C): None (N)
• Integrity (I): High (H)
• Availability (A): High (H)

Estimated CVSS v3.1 Score: 9.1 (Critical)

Threat Level: Critical – Remote, unauthenticated file manipulation with no user interaction required.

Deep Dive & Mechanics

The vulnerability resides in the permission assignment logic of Owl opds 2.2.0.4. The application fails to properly restrict access to critical resources, such as configuration files, user data, or system files. By sending a specially crafted network request (likely an HTTP request with manipulated parameters or paths), an attacker can bypass intended access controls and perform file operations (read, write, delete) on the server.

Root Cause: The application does not validate or enforce proper permissions on file system operations triggered via network requests. This could be due to missing authorization checks, insecure direct object references (IDOR), or improper handling of file paths (path traversal).

Attack Scenario:

1. Attacker identifies the Owl opds service running on a target.
2. Attacker sends a crafted HTTP request (e.g., POST or GET) with a manipulated parameter that specifies a file path.
3. The server processes the request without verifying the user's permissions or sanitizing the path.
4. The attacker can overwrite configuration files, inject malicious code, or delete critical data.

Vulnerable vs. Patched Code

Since no patch is available, a hypothetical fix would involve:

Vulnerable Code (Conceptual):

@app.route('/file_operation', methods=['POST'])
def file_operation():
    filename = request.form['filename']
    action = request.form['action']
    if action == 'delete':
        os.remove(filename)
    elif action == 'write':
        content = request.form['content']
        with open(filename, 'w') as f:
            f.write(content)
    return "Operation completed"

Patched Code (Conceptual):

import os
from pathlib import Path

ALLOWED_DIR = Path('/var/owl_opds/data')

@app.route('/file_operation', methods=['POST'])
def file_operation():
    filename = request.form['filename']
    action = request.form['action']
    # Sanitize path
    safe_path = ALLOWED_DIR / filename
    safe_path = safe_path.resolve()
    if not str(safe_path).startswith(str(ALLOWED_DIR)):
        return "Access denied", 403
    # Check permissions
    if not current_user.has_permission('file_operation'):
        return "Forbidden", 403
    if action == 'delete':
        os.remove(safe_path)
    elif action == 'write':
        content = request.form['content']
        with open(safe_path, 'w') as f:
            f.write(content)
    return "Operation completed"

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Deploy Owl opds 2.2.0.4 in a controlled environment (e.g., Docker container).
2. Expose the service on a local network.

Exploitation Steps:

1. Identify the vulnerable endpoint (e.g., /file_operation or similar).
2. Craft a request to manipulate a critical file:

   curl -X POST http://target:8080/file_operation \
     -d "filename=../../etc/passwd&action=write&content=attacker:x:0:0:root:/root:/bin/bash"
   

3. Verify the file was modified by reading it:

   curl -X POST http://target:8080/file_operation \
     -d "filename=../../etc/passwd&action=read"
   

Note: This is a conceptual example. Actual exploitation may require different parameters or methods.

Blue Team

Detection:

• Monitor for unusual file access patterns, especially to sensitive directories (e.g., /etc, /var/www).
• Look for HTTP requests with path traversal sequences (../) in parameters.
• Alert on file modification events for critical system files.

Hunting:

• Search logs for requests to endpoints like /file_operation or similar.
• Check for unexpected changes to configuration files or user accounts.

Indicators of Compromise (IOCs)

• Network:
  • HTTP requests containing path traversal patterns (../, %2e%2e%2f).
  • Requests to unusual endpoints (e.g., /file_operation, /admin/file).
• File System:
  • Unexpected modifications to /etc/passwd, /etc/shadow, or application config files.
  • New files in sensitive directories (e.g., /tmp/exploit.sh).
• Process:
  • Unusual child processes spawned by the Owl opds service (e.g., bash, python).

Detection Engineering

YARA Rule

rule CVE_2026_26101_Owl_FileManipulation {
    meta:
        description = "Detects attempts to exploit CVE-2026-26101 via path traversal in HTTP requests"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-26101"
    strings:
        $path_traversal = /(\.\.\/|\.\.\\|%2e%2e%2f|%2e%2e%5c)/ nocase
        $sensitive_file = /(etc\/passwd|etc\/shadow|boot\.ini|web\.config)/ nocase
        $file_op = /file_operation|file_upload|file_delete/ nocase
    condition:
        any of ($path_traversal) and any of ($sensitive_file) and any of ($file_op)
}

Sigma Rule

title: CVE-2026-26101 Exploitation Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP requests attempting to exploit file manipulation vulnerability in Owl opds
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains:
            - 'file_operation'
            - 'file_upload'
            - 'file_delete'
        cs-uri-query|re: '(\.\.\/|\.\.\\|%2e%2e%2f|%2e%2e%5c)'
    condition: selection
falsepositives:
    - Legitimate file management operations within allowed directories
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2026-26101 - Owl opds File Manipulation Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"file_operation"; http_uri;
    pcre:"/(\.\.\/|\.\.\\|%2e%2e%2f|%2e%2e%5c)/i";
    sid:1000001;
    rev:1;
    reference:cve,2026-26101;
    classtype:attempted-admin;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate the affected system from untrusted networks.
2. Disable any file operation endpoints if possible.
3. Monitor logs for signs of exploitation.

Long-term Fix:

• Apply proper input validation and path sanitization.
• Implement strict access controls (e.g., role-based permissions).
• Use a whitelist of allowed directories for file operations.
• Upgrade to a patched version once available.

Workaround:

• Deploy a Web Application Firewall (WAF) with rules to block path traversal attempts.
• Restrict network access to the Owl opds service using firewall rules.

Report generated by Valters IT DevSecOps & CTI Expert System