This attack targets libraries or shared code modules which are vulnerable to buffer overflow attacks. An attacker who has access to an API may try to embed malicious code in the API function call and exploit a buffer overflow vulnerability in the function's implementation. All clients that make use of the code library thus become vulnerable by association. This has a very broad effect on security across a system, usually affecting more than one software process.
Attack Execution Flow
An attacker can call an API exposed by the target host.
On the probing stage, the attacker injects malicious code using the API call and observes the results. The attacker's goal is to uncover a buffer overflow vulnerability.
The attacker finds a buffer overflow vulnerability, crafts malicious code and injects it through an API call. The attacker can at worst execute remote code on the target host.
The target host exposes an API to the user.
One or more API functions exposed by the target host has a buffer overflow vulnerability.
Typical Likelihood of Exploit
Methods of Attack
A buffer overflow in the FreeBSD utility setlocale (found in the libc module) puts many programs at risk all at once.
A buffer overflow in the Xt library of the X windowing system allows local users to execute commands with root privileges.
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.
Solutions and Mitigations
Use a language or compiler that performs automatic bounds checking.
Use secure functions not vulnerable to buffer overflow.
If you have to use dangerous functions, make sure that you do boundary checking.
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.
Use OS-level preventative functionality. Not a complete solution.
DoS: crash / exit / restart
Execute unauthorized code or commands
Run Arbitrary Code
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.