The way the attacker has escalated the privilege to root through taking advantage of the Sudo IPTables

Overview

As you may know, in many Linux systems, administrators often configure sudo to grant users the ability to run specific commands without a password. One common tool given such permission is iptables, used to configure the firewall. But what happens if this permission is exploited to gain full root access?

This article will analyze the process of exploiting a seemingly harmless sudo permission to escalate privileges to root. Through this, we will see the importance of understanding the behavior of system commands and managing sudo policies more carefully.

Once attackers gain root access, they can easily:

• Manipulate and control all processes running on the system, without user restrictions.

• Change network settings, open ports, run packet-sniffing programs, adjust iptables, spoof MAC/IP, etc.

• Sometimes "show off" their hacking skills or system control to friends—because root is not just technical, it's also a style.

Execution Context

We need to understand that iptables configurations are stored using the following tools:

• iptables-save: exports the entire current iptables configuration as text.

• iptables-restore: reads the configuration file and re-establishes the entire iptables setup.

The question is: does iptables support arbitrary code execution?

The answer is indirectly yes, through the xtables-addons module or by interacting with special libraries or files in /proc. However, the more common and simpler way is to use iptables to overwrite root files or enable arbitrary code execution by combining it with a shell script.

Exploitation Method

In recorded campaigns, analysts have identified two main exploitation techniques for escalating privileges to root.

Technique 1: Overwriting /etc/passwd via iptables-save

• As mentioned above, iptables allows comments to be added to rules through the comment module. When using iptables-save, these comments are recorded in the output. By inserting a fake line into the comment and overwriting /etc/passwd, an attacker can create a root user with a password of their choice.

• Initially, the attacker will create an encrypted password for root. The result will be an encrypted string.

  

• Then the attacker will use the newly created encrypted string to deploy the fake line for root and add a Rule with a Comment containing the fake line.

  

  

• Next, the attacker will use sudo to overwrite the /etc/passwd file with iptables-save and finally be able to log in with the newly created root user.

  

Technique 2: Arbitrary Command Execution via --modprobe

• When iptables needs to load a kernel module that isn't available, it uses modprobe to load that module. If it's possible to specify an arbitrary modprobe program, commands can be executed with root privileges.

• Initially, the attacker will create a malicious script on the system.

  

• The next step is for the attacker to use iptables with --modprobe to point to the script that was just created.

  

• And finally, the attacker can execute a shell with root privileges.

Once the privilege escalation process is complete, the attacker will remove traces by deleting the added iptables rules and removing the files and scripts created during the exploitation process.

Conclusion

Sudo privileges for iptables may seem harmless, but in reality, they can be exploited to gain root access on the system. Through this article, you have seen:

• How to understand and analyze sudo privileges.

• How to exploit iptables to write files or execute malicious code.

• Real-world privilege escalation techniques.

Therefore, organizations and users should always carefully check sudo privileges and system configurations to avoid falling victim to such exploits.

Recommendations

1. Do not grant sudo directly to iptables

   • Remove sudo access for iptables unless absolutely necessary.

   • If required, use alternative solutions such as:

     • iptables wrapper script (a secure script that only allows a few basic rules).

     • Use sudoers with specific options to limit commands.

2. Properly configure sudoers

   • Use NOEXEC to block shell calls from programs:

     • Defaults!/sbin/iptables noexec

   • Restrict executable paths (secure_path):

     • Defaults secure_path="/usr/sbin:/usr/bin:/sbin:/bin"

3. Assign permissions appropriately

   • Do not grant ALL permissions if not necessary.

   • Separate roles: network admin users should only have network permissions, not system permissions.

   • Use sudo by group instead of individual users.

4. Regularly update the operating system and kernel

   • sudo apt update && sudo apt upgrade -y # Debian/Ubuntu

   • sudo dnf update # RHEL/Fedora

References

1. Shielder - A Journey From <code>sudo iptables</code> To Local Privilege Escalation

2. Privilege Escalation on Unix – Lisandre