CAPEC 100

Summary

Attack Execution Flow

1. The attacker identifies a buffer to target. Buffer regions are either allotted on the stack or the heap, and the exact nature of attack would vary depending on the location of the buffer

2. Next, the attacker identifies an injection vector to deliver the excessive content to the targeted buffer.

3. The attacker 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 attacker will craft a set of content that not only overflows the targeted buffer but does so in such a way that the overwritten return address is replaced with one of the attacker's choosing which points to code injected by the attacker.

4. The attacker injects the content into the targeted software.

5. Upon successful exploitation, the system either crashes or control of the program is returned to a location of the attacker's choice. This can result in execution of arbitrary code or escalated privileges, depending upon the exploited target.

Likelihood: High

Description

Description

Skill or Knowledge Level: 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.

Skill or Knowledge Level: High

In cases of directed overflows, where the motive is to divert the flow of the program or application as per the attacker's bidding, high level skills are required. This may involve detailed knowledge of the target system architecture and kernel.

The attacker sends in overtly long input in variables under his control. If the target system or application handles it gracefully, the attack becomes difficult. However, an error condition or a system crash point to a high likelihood of successful exploitation.

In cases where the attack is directed at a particular system or application, such as an operating system or a web server, the attacker can refer to system architecture and design documentation to figure out the exact point of injection and exploitation.

An attack designed to leverage a buffer overflow and redirect execution as per the attacker'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 attacker would have resorted to a few hit-or-miss attempts that will be recorded in the system event logs, if they exist.

A buffer overflow attack itself is pretty difficult to obfuscate. There, however, exist fairly advanced techniques to ofuscate the payload, in order to bypass an intrusion detection system or filtering, either in the application or by means of an application firewall of some sorts.

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.

Utilize static source code analysis tools to identify potential buffer overflow weaknesses in the software.

All user-controllable input must be strictly validated for enforcement of length and semantic checks

All exception conditions (such as ArrayIndexOutOfBounds) in applications must be gracefully handled through use of available exception handling mechanisms.

All applications and processes must be run with minimum privileges necessary so as to avoid an escalation of privilege in case of a successful exploit.