This attack targets command-line utilities available in a number of shells. An attacker can leverage a vulnerability found in a command-line utility to escalate privilege to root.
Attack Execution Flow
Attacker identifies command utilities exposed by the target host.
On the probing stage, the attacker interacts with the command utility and observes the results of its input. The attacker's goal is to uncover a buffer overflow in the command utility. For instance the attacker may find that input data are not properly validated.
The attacker finds a buffer overflow vulnerability in the command utility and tries to exploit it. He crafts malicious code and injects it using the command utility. The attacker can at worst execute remote code on the target host.
The target host exposes a command-line utility to the user.
The command-line utility exposed by the target host has a buffer overflow vulnerability that can be exploited.
Typical Likelihood of Exploit
Methods of Attack
Attack Example: HPUX passwd
A buffer overflow in the HPUX passwd command allows local users to gain root privileges via a command-line option.
Attack Example: Solaris getopt
A buffer overflow in Solaris's getopt command (found in libc) allows local users to gain root privileges via a long argv.
Attacker Skills or Knowledge Required
Skill or Knowledge Level: Low
An attacker can simply overflow a buffer by inserting a long string into an attacker-modifiable injection vector. The result can be a DoS.
Skill or Knowledge Level: High
Exploiting a buffer overflow to inject malicious code into the stack of a software system or even the heap can require a higher skill level.
The attacker can probe for services available on the target host. Many services may expose a command utility. For instance Telnet is a service which can be invoked through a command shell.
Solutions and Mitigations
Carefully review the service's implementation before making it available to user. For instance you can use manual or automated code review to uncover vulnerabilities such as buffer overflow.
Use a language or compiler that performs automatic bounds checking.
Use an abstraction library to abstract away risky APIs. Not a complete solution.
Compiler-based canary mechanisms such as StackGuard, ProPolice and the Microsoft Visual Studio /GS flag. Unless this provides automatic bounds checking, it is not a complete solution.
Operational: Use OS-level preventative functionality. Not a complete solution.
Apply the latest patches to your user exposed services. This may not be a complete solution, especially against a zero day attack.
Do not unnecessarily expose services.
Gain privileges / assume identity
Execute unauthorized code or commands
Run Arbitrary Code
DoS: crash / exit / restart
The user supplied data.
The buffer overrun by the attacker.
When the function returns control to the main program, it jumps to the return address portion of the stack frame. Unfortunately that return address may have been overwritten by the overflowed buffer and the address may contain a call to a privileged command or to a malicious code.