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CAPEC-24:Filter Failure through Buffer Overflow

Attack Pattern ID:24

Version:v3.9

Attack Pattern Name:Filter Failure through Buffer Overflow

Abstraction:Detailed

Status:Draft

Likelihood of Attack:High

Typical Severity:High

Details Content History Related Weaknesses Reports

▼Description

In this attack, the idea is to cause an active filter to fail by causing an oversized transaction. An attacker may try to feed overly long input strings to the program in an attempt to overwhelm the filter (by causing a buffer overflow) and hoping that the filter does not fail securely (i.e. the user input is let into the system unfiltered).

▼Relationships

Nature	Type	ID	Name
ChildOf	S	100	Overflow Buffers

Nature: ChildOf

Type: Standard

ID: 100

Name: Overflow Buffers

▼Execution Flow

Explore

Survey

The attacker surveys the target application, possibly as a valid and authenticated user

Technique
Spidering web sites for inputs that involve potential filtering
Brute force guessing of filtered inputs

Experiment

Attempt injections

Try to feed overly long data to the system. This can be done manually or a dynamic tool (black box) can be used to automate this. An attacker can also use a custom script for that purpose.

Technique
Brute force attack through black box penetration test tool.
Fuzzing of communications protocols
Manual testing of possible inputs with attack data.

Monitor responses

Watch for any indication of failure occurring. Carefully watch to see what happened when filter failure occurred. Did the data get in?

Technique
Boron tagging. Choose clear attack inputs that are easy to notice in output. In binary this is often 0xa5a5a5a5 (alternating 1s and 0s). Another obvious tag value is all zeroes, but it is not always obvious what goes wrong if the null values get into the data.
Check Log files. An attacker with access to log files can look at the outcome of bad input.

Exploit

Abuse the system through filter failure

An attacker writes a script to consistently induce the filter failure.

Technique
DoS through filter failure. The attacker causes the system to crash or stay down because of its failure to filter properly.
Malicious code execution. An attacker introduces a malicious payload and executes arbitrary code on the target system.
An attacker can use the filter failure to introduce malicious data into the system and leverage a subsequent SQL injection, Cross Site Scripting, Command Injection or similar weakness if it exists.

▼Prerequisites

Ability to control the length of data passed to an active filter.

▼Skills Required

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.

▼Indicators

Many exceptions are thrown by the application's filter modules in a short period of time. Check the logs. See if the probes are coming from the same IP address.

▼Consequences

Scope	Likelihood	Impact	Note
Integrity	N/A	Modify Data	N/A
ConfidentialityIntegrityAvailability	N/A	Execute Unauthorized Commands	Run Arbitrary Code
ConfidentialityAccess ControlAuthorization	N/A	Bypass Protection Mechanism	N/A
Availability	N/A	Unreliable Execution	N/A

Scope: Integrity

Likelihood: N/A

Impact: Modify Data

Note: N/A

Scope: Confidentiality, Integrity, Availability

Likelihood: N/A

Impact: Execute Unauthorized Commands

Note: Run Arbitrary Code

Scope: Confidentiality, Access Control, Authorization

Likelihood: N/A

Impact: Bypass Protection Mechanism

Note: N/A

Scope: Availability

Likelihood: N/A

Impact: Unreliable Execution

Note: N/A

▼Mitigations

Make sure that ANY failure occurring in the filtering or input validation routine is properly handled and that offending input is NOT allowed to go through. Basically make sure that the vault is closed when failure occurs.

Pre-design: Use a language or compiler that performs automatic bounds checking.

Pre-design through Build: 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.

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

Design: Use an abstraction library to abstract away risky APIs. Not a complete solution.

▼Example Instances

▼Related Weaknesses

ID	Name
CWE-118	Incorrect Access of Indexable Resource ('Range Error')
CWE-119	Improper Restriction of Operations within the Bounds of a Memory Buffer
CWE-120	Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
CWE-20	Improper Input Validation
CWE-680	Integer Overflow to Buffer Overflow
CWE-697	Incorrect Comparison
CWE-733	Compiler Optimization Removal or Modification of Security-critical Code
CWE-74	Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')