Exploiting Misconfigured ACLs: From Privilege Escalation to Domain Compromise

Table of Contents#

Introduction
How Does the ACL Abuse Attack Work?
Practical Examples and How to Execute the Attack
Example 1: Abusing File Permissions with Misconfigured ACLs
- Scenario
- Steps to Exploit
Example 2: Exploiting Executable Permissions on Scripts
- Scenario
- Steps to Exploit
Example 3: Exploiting Setuid Files for Privilege Escalation
- Scenario
- Steps to Exploit
Example 4: Abusing Network ACLs
- Scenario
- Steps to Exploit

Introduction#

An Access Control List (ACL) is a set of rules that defines permissions for accessing resources in a system, such as files, directories, or network services. When ACLs are misconfigured, they can allow unauthorized users to access or manipulate resources they shouldn’t have access to. The Abusing ACL attack leverages these misconfigurations to escalate privileges, access sensitive data, or execute unauthorized actions.

How Does the ACL Abuse Attack Work?#

Misconfigured ACLs: If ACLs are not properly set, they might allow unintended users or processes to read, write, or execute files and commands. Attackers can exploit these weaknesses to gain unauthorized access.
Escalating Privileges: An attacker can exploit improperly configured ACLs to gain higher privileges, such as reading sensitive files, executing commands as a superuser (root or administrator), or modifying critical configurations.
Accessing Sensitive Data: Misconfigured ACLs can allow attackers to access confidential files (e.g., configuration files, password files) that would normally be restricted.

Practical Examples and How to Execute the Attack#

Let’s break down the attack with some practical examples, and I’ll guide you on how to execute the attack in a controlled penetration testing environment.

Example 1: Abusing File Permissions with Misconfigured ACLs#

Scenario#

You are testing a web server, and you discover that the ACL for a sensitive file (e.g., config.php) is misconfigured. The ACL might be set to allow all users to read or write to this file, which should not be the case.

Steps to Exploit#

Check the ACL of the File: Use tools like getfacl (on Linux) to check the ACL of the file.
```
getfacl /path/to/config.php
```
- If the output shows that the file is readable or writable by unauthorized users, then the ACL is misconfigured.
Access the File: If you have unauthorized access, you can read the file to find sensitive information such as database credentials, API keys, etc.
```
cat /path/to/config.php
```
- This will allow you to view the file contents if ACLs are improperly set.
Modify the File (If Writable): If the file is writable, you can inject malicious code, change settings, or delete important information.
```
echo "malicious_code" > /path/to/config.php
```

Example 2: Exploiting Executable Permissions on Scripts#

Scenario#

There are executable scripts (e.g., PHP, CGI) on the server that can be executed by users with improper ACLs. These scripts might allow unauthorized users to execute commands on the server.

Steps to Exploit#

Identify Executable Files: First, search for files with executable permissions. You can use the following command to find all executable files in a directory:
```
find /path/to/scripts -type f -perm /u+x
```
- This will list all files that have execute permissions for the user.
Check for Vulnerabilities: If the script allows user input, such as form fields or URL parameters, you can attempt command injection or other attacks to gain control over the system.
Exploit the Script: If you find a vulnerable script, you can try to execute arbitrary commands. For example, if a PHP script allows input via a URL, you might attempt to inject a command.
Example URL injection:
```
http://target.com/script.php?cmd=ls
```
- If the script is not properly sanitized, it may execute the ls command on the server and display the directory contents.

Example 3: Exploiting Setuid Files for Privilege Escalation#

Scenario#

The system has setuid binaries, which execute with the privileges of the file owner (often root). If these binaries are misconfigured in ACLs, a user can execute them and escalate their privileges.

Steps to Exploit#

Find Setuid Files: Use the following command to find all setuid files on the system:
```
find / -type f -perm -4000
```
- Setuid files are often used for tasks that require elevated privileges, such as system administration tasks.
Exploit Setuid Binaries: If you find a setuid binary like /bin/bash, you can execute it with root privileges. For example:
```
/bin/bash
```

Example 4: Abusing Network ACLs#

Scenario#

You discover that a network service (e.g., MySQL, PostgreSQL) has misconfigured ACLs, allowing unauthorized users to connect to the service.

Steps to Exploit#

Scan for Open Ports: Use nmap to scan for open ports and services on the target machine.
```
nmap -p 3306 192.168.1.100
```
- If you find an open MySQL port (for example), it might be vulnerable.
Check for Misconfigured ACLs: If the service has ACLs that allow connections from unauthorized IP addresses, you can attempt to connect to the service and exploit it.
Access the Database: If you have the correct credentials or the service is misconfigured to allow anonymous access, you can access and manipulate the database.
```
mysql -h 192.168.1.100 -u root -p
```
Once inside, you can execute SQL queries to read, modify, or delete sensitive data.

Happy Hacking Broo