Common Attack Pattern Enumeration and Classification

Common Attack Pattern Enumeration and Classification

10

High

The application uses environment variables.

An environment variable exposed to the user is vulnerable to a buffer overflow.

The vulnerable environment variable uses untrusted data.

Tainted data used in the environment variables is not properly validated. For instance boundary checking is not done before copying the input data to a buffer.

High

• Injection

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. 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.

While interacting with a system an attacker would typically investigate for environment variables that can be overwritten. The more a user knows about a system the more likely she will find a vulnerable environment variable.

On a web environment, the attacker can read the client side code and search for environment variables that can be overwritten.

There are tools such as Sharefuzz (http://sharefuzz.sourceforge.net/) which is an environment variable fuzzer for Unix that support loading a shared library. Attackers can use such tools to uncover a buffer overflow in an environment variable.

If the application does bound checking, it should fail when the data source is larger than the size of the destination buffer. If the application's code is well written, that failure should triger an alert.

Do not expose environment variable to the user.

Do not use untrusted data in your environment variables.

Use a language or compiler that performs automatic bounds checking

There are tools such as Sharefuzz (http://sharefuzz.sourceforge.net/) which is an environment variable fuzzer for Unixes that support loading a shared library. You can use Sharefuzz to determine if you are exposing an environment variable vulnerable to buffer overflow.

• Denial of Service
• Run Arbitrary Code
• Information Leakage
• Data Modification
• Privilege Escalation

The user modifiable environment variable.

User supplied data potentially containing malicious code.

When the subroutine which uses the environment variable 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.

The most common is remote code execution.

• Reluctance to trust

• Bound checking should be performed when copying data to a buffer.

Penetration

G. Hoglund and G. McGraw. Exploiting Software: How to Break Code. Addison-Wesley, February 2004.

CWE – Buffer Errors