COMMON ATTACK PATTERN ENUMERATION AND CLASSIFICATIONLive MITRE record

CAPEC-100

Overflow Buffers

Buffer Overflow attacks target improper or missing bounds checking on buffer operations, typically triggered by input injected by an adversary. As a consequence, an adversary is able to write past the boundaries of allocated buffer regions in memory, causing a program crash or potentially redirection of execution as per the adversaries' choice.

Abstraction

Standard

Typical severity

Very High

Likelihood of attack

High

Understand the attack

What is this attack pattern?

Buffer Overflow attacks target improper or missing bounds checking on buffer operations, typically triggered by input injected by an adversary. As a consequence, an adversary is able to write past the boundaries of allocated buffer regions in memory, causing a program crash or potentially redirection of execution as per the adversaries' choice.

Execution flow

How does the attack proceed, step by step?

1

Explore

Identify target application

The adversary identifies a target application or program to perform the buffer overflow on. Adversaries often look for applications that accept user input and that perform manual memory management.
2

Experiment

Find injection vector

The adversary identifies an injection vector to deliver the excessive content to the targeted application's buffer.

Techniques used

  • Provide large input to a program or application and observe the behavior. If there is a crash, this means that a buffer overflow attack is possible.

Craft overflow content

The adversary crafts the content to be injected. If the intent is to simply cause the software to crash, the content need only consist of an excessive quantity of random data. If the intent is to leverage the overflow for execution of arbitrary code, the adversary crafts the payload in such a way that the overwritten return address is replaced with one of the adversary's choosing.

Techniques used

  • Create malicious shellcode that will execute when the program execution is returned to it.
  • Use a NOP-sled in the overflow content to more easily "slide" into the malicious code. This is done so that the exact return address need not be correct, only in the range of all of the NOPs
3

Exploit

Overflow the buffer

Using the injection vector, the adversary injects the crafted overflow content into the buffer.

Requirements

What does the attack require?

Prerequisites

  • Targeted software performs buffer operations.
  • Targeted software inadequately performs bounds-checking on buffer operations.
  • Adversary has the capability to influence the input to buffer operations.

Skills required

  • Low: In most cases, overflowing a buffer does not require advanced skills beyond the ability to notice an overflow and stuff an input variable with content.
  • High: In cases of directed overflows, where the motive is to divert the flow of the program or application as per the adversaries' bidding, high level skills are required. This may involve detailed knowledge of the target system architecture and kernel.

Resources required

  • None: No specialized resources are required to execute this type of attack. Detecting and exploiting a buffer overflow does not require any resources beyond knowledge of and access to the target system.

Detection

What are the indicators of the attack?

An attack designed to leverage a buffer overflow and redirect execution as per the adversary's bidding is fairly difficult to detect. An attack aimed solely at bringing the system down is usually preceded by a barrage of long inputs that make no sense. In either case, it is likely that the adversary would have resorted to a few hit-or-miss attempts that will be recorded in the system event logs, if they exist.

Impact

What does a successful attack lead to?

Unreliable Execution

Affected scopes: Availability

Execute Unauthorized Commands

Affected scopes: Confidentiality, Integrity, Availability

Gain Privileges

Affected scopes: Confidentiality, Access Control, Authorization

Defence

How is it prevented and mitigated?

1
Use a language or compiler that performs automatic bounds checking.
2
Use secure functions not vulnerable to buffer overflow.
3
If you have to use dangerous functions, make sure that you do boundary checking.
4
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.
5
Use OS-level preventative functionality. Not a complete solution.
6
Utilize static source code analysis tools to identify potential buffer overflow weaknesses in the software.

Real world

MITRE example instances

Example instance 1Detail
The most straightforward example is an application that reads in input from the user and stores it in an internal buffer but does not check that the size of the input data is less than or equal to the size of the buffer. If the user enters excessive length data, the buffer may overflow leading to the application crashing, or worse, enabling the user to cause execution of injected code.
Example instance 2Detail
Many web servers enforce security in web applications through the use of filter plugins. An example is the SiteMinder plugin used for authentication. An overflow in such a plugin, possibly through a long URL or redirect parameter, can allow an adversary not only to bypass the security checks but also execute arbitrary code on the target web server in the context of the user that runs the web server process.