COMMON ATTACK PATTERN ENUMERATION AND CLASSIFICATIONLive MITRE record

CAPEC-46

Overflow Variables and Tags

This type of attack leverages the use of tags or variables from a formatted configuration data to cause buffer overflow. The adversary crafts a malicious HTML page or configuration file that includes oversized strings, thus causing an overflow.

Abstraction

Detailed

Typical severity

High

Likelihood of attack

High

Understand the attack

What is this attack pattern?

Execution flow

How does the attack proceed, step by step?

Explore

Identify target application

The adversary identifies a target application or program to perform the buffer overflow on. Adversaries look for applications or programs that accept formatted files, such as configuration files, as input.

Experiment

Find injection vector

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

Techniques used

Knowing the type of file that an application takes as input, the adversary takes a normal input file and modifies a single variable or tag to contain a large amount of data. If there is a crash, this means that a buffer overflow attack is possible. The adversary will keep changing single variables or tags one by one until they see a change in behavior.

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

Exploit

Overflow the buffer

The adversary will upload the crafted file to the application, causing a buffer overflow.

Requirements

What does the attack require?

Prerequisites

The target program consumes user-controllable data in the form of tags or variables.
The target program does not perform sufficient boundary checking.

Skills required

Low: An adversary can simply overflow a buffer by inserting a long string into an adversary-modifiable injection vector. The result can be a DoS.
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.

Resources required

Not stated in the MITRE record.

Impact

What does a successful attack lead to?

Unreliable Execution

Affected scopes: Availability

Execute Unauthorized Commands

Affected scopes: Confidentiality, Integrity, Availability

Read Data

Affected scopes: Confidentiality

Modify Data

Affected scopes: Integrity

Defence

How is it prevented and mitigated?

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.

Use OS-level preventative functionality. Not a complete solution.

Do not trust input data from user. Validate all user input.

Real world

MITRE example instances

Example instance 1Detail

A buffer overflow vulnerability exists in the Yamaha MidiPlug that can be accessed via a Text variable found in an EMBED tag. See also: CVE-1999-0946

Example instance 2Detail

A buffer overflow in Exim allows local users to gain root privileges by providing a long :include: option in a .forward file. See also: CVE-1999-0971