CAPEC 28

Summary

Attack Execution Flow

1. Observe communication and inputs:

   The fuzzing attacker observes the target system looking for inputs and communications between modules, subsystems, or systems.

   Attack Step Techniques

   ID	Attack Step Technique Description	Environments
   1	Network sniffing. Using a network sniffer such as wireshark, the attacker observes communications into and out of the target system.	env-Web env-ClientServer env-Peer2Peer env-CommProtocol
   2	Monitor API execution. Using a tool such as ktrace, strace, APISpy, or another debugging tool, the attacker observes the system calls and API calls that are made by the target system, and the nature of their parameters.	env-Local env-Embedded
   3	Observe inputs using web inspection tools (OWASP's WebScarab, Paros, TamperData, TamperIE, etc.)	env-Web

   Outcomes

   ID	type	Outcome Description
   1	Success	The attacker creates a list of unique communications packets, messages, inputs, API calls or other actions the software takes.

   Security Controls

   ID	type	Security Control Description
   1	Detective	Alert on promiscuous mode. Some network devices (switches, hubs) or monitoring stations (e.g., IDS) can detect and alert when a station in the network is passively eavesdropping.
   2	Preventative	Some production hardware (for embedded environments) can have debugging disabled on the hardware.
   3	Preventative	Techniques exist to insert no-ops and other null branches that thwart basic attempts to execute software stepwise in a debugger.

1. Generate fuzzed inputs:

   Given a fuzzing tool, a target input or protocol, and limits on time, complexity, and input variety, generate a list of inputs to try. Although fuzzing is random, it is not exhaustive. Parameters like length, composition, and how many variations to try are important to get the most cost-effective impact from the fuzzer.

   Attack Step Techniques

   ID	Attack Step Technique Description	Environments
   1	Boundary cases. Generate fuzz inputs that attack boundary cases of protocol fields, inputs, or other communications limits. Examples include 0xff and 0x00 for single-byte inputs. In binary situations, approach each bit of an individual field with on and off (e.g., 0x80).	env-All
   2	Attempt arguments to system calls or APIs. The variations include payloads that, if they were successful, could lead to a compromise on the system.	env-Local env-Embedded

   Security Controls

   ID	type	Security Control Description
   1	Detective	Log unexpected parameters to API calls or system calls.
   2	Preventative	Profile the software's expected use of system calls. Use a sandboxing technique to restrict its API calls to the expected patterns.
   3	Preventative	SSL or other link-layer encryption techniques (VPN, 802.11x, etc.) can impair simple observation and require a would-be attacker to work much harder to get information about the operation of the software..

2. Observe the outcome:

   Observe the outputs to the inputs fed into the system by fuzzers and see if anything interesting happens. If failure occurs, determine why that happened. Figure out the underlying assumption that was invalidated by the input.

   Indicators

   ID	type	Indicator Description	Environments
   1	Positive	The software produces an indicator that the attacker can see (error message, altered error state in a protocol, etc.).	env-All
   2	Positive	The previous step led to plausible, practical fuzz inputs.	env-All

   Outcomes

   ID	type	Outcome Description
   1	Success	If the software's indicators (error messages, etc.) vary clearly based on the attacker's input, then the attacker has a sufficient starting point for customizing his attack.
   2	Failure	The attacker is unable to induce unexpected failures or output based fuzzed inputs.

1. Craft exploit payloads:

   Put specially crafted input into the system that leverages the weakness identified through fuzzing and allows to achieve the goals of the attacker. Fuzzers often reveal ways to slip through the input validation filters and introduce unwanted data into the system.

   Attack Step Techniques

   ID	Attack Step Technique Description	Environments
   1	Identify and embed shellcode for the target system.	env-All
   2	Embed higher level attack commands in the payload. (e.g., SQL, PHP, server-side includes, etc.)	env-Web env-CommProtocol env-Peer2Peer env-ClientServer
   3	Induce denial of service by exploiting resource leaks or bad error handling.	env-All

   Security Controls

   ID	type	Security Control Description
   1	Detective	Monitor system logs and alert on unusual activity. Most shellcode and unusual activity appears in logs.

Likelihood: High

Description

Skill or Knowledge Level: Low

There is a wide variety of fuzzing tools available.

A lot of invalid data is fed to the system. Data that cannot have been generated through a legitimate transaction/request. Data is coming into the system within a short period of time and potentially from the same IP.

Take pauses between fuzzing attempts (may not be very practical). Spoof IP addresses so that it does not look like all data is coming from the same source.

Test to ensure that the software behaves as per specification and that there are no unintended side effects. Ensure that no assumptions about the validity of data are made.

Use fuzz testing during the software QA process to uncover any surprises, uncover any assumptions or unexpected behavior.