How does a Filter Failure through Buffer Overflow attack work?

It typically unfolds over 4 phases. It begins with: [Survey] The attacker surveys the target application, possibly as a valid and authenticated user

How do you prevent CAPEC-24?

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.

What weaknesses does CAPEC-24 target?

CAPEC-24 exploits 8 CWE weaknesses, including CWE-20 (Improper Input Validation), CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')), CWE-118 (Incorrect Access of Indexable Resource ('Range Error')), CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer).

How severe is CAPEC-24?

MITRE rates CAPEC-24 as High severity with high likelihood of attack.

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Detailed attack pattern

Draft

CAPEC-24: Filter Failure through Buffer Overflow

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).

Last updated June 1, 2026

High

Typical severity

Per MITRE

High

Likelihood of attack

Per MITRE

8

Related weaknesses

CWEs this targets

Detailed

Abstraction

MITRE classification

Overview

CAPEC-24 (Filter Failure through Buffer Overflow) is a detailed-level attack pattern catalogued by MITRE in the Common Attack Pattern Enumeration and Classification (CAPEC). It describes a recurring method attackers use to exploit software weaknesses.

How the attack works

The phases an attacker typically follows.

Step 1
Explore
[Survey] The attacker surveys the target application, possibly as a valid and authenticated user
- Spidering web sites for inputs that involve potential filtering
- Brute force guessing of filtered inputs
Step 2
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.
- Brute force attack through black box penetration test tool.
- Fuzzing of communications protocols
- Manual testing of possible inputs with attack data.
Step 3
Experiment
[Monitor responses] Watch for any indication of failure occurring. Carefully watch to see what happened when filter failure occurred. Did the data get in?
- 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.
Step 4
Exploit
[Abuse the system through filter failure] An attacker writes a script to consistently induce the filter failure.
- 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.

What the attacker needs

Prerequisites

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

Skills required

Low skill: 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 skill: 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.

Consequences

What a successful CAPEC-24 attack can achieve.

Modify Data

Affects: Integrity

Execute Unauthorized Commands

Affects: Confidentiality, Integrity, Availability

Run Arbitrary Code

Bypass Protection Mechanism

Affects: Confidentiality, Access Control, Authorization

Unreliable Execution

Affects: Availability

How to mitigate it

Defenses that reduce the risk of CAPEC-24.

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.

How to detect it

Indicators that this attack may be underway.

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.

Examples

Sending in arguments that are too long to cause the filter to fail open is one instantiation of the filter failure attack. The Taylor UUCP daemon is designed to remove hostile arguments before they can be executed. If the arguments are too long, however, the daemon fails to remove them. This leaves the door open for attack.

A filter is used by a web application to filter out characters that may allow the input to jump from the data plane to the control plane when data is used in a SQL statement (chaining this attack with the SQL injection attack). Leveraging a buffer overflow the attacker makes the filter fail insecurely and the tainted data is permitted to enter unfiltered into the system, subsequently causing a SQL injection.

Audit Truncation and Filters with Buffer Overflow. Sometimes very large transactions can be used to destroy a log file or cause partial logging failures. In this kind of attack, log processing code might be examining a transaction in real-time processing, but the oversized transaction causes a logic branch or an exception of some kind that is trapped. In other words, the transaction is still executed, but the logging or filtering mechanism still fails. This has two consequences, the first being that you can run transactions that are not logged in any way (or perhaps the log entry is completely corrupted). The second consequence is that you might slip through an active filter that otherwise would stop your attack.

Frequently asked questions

Common questions about CAPEC-24.

What is CAPEC-24?: 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).
How does a Filter Failure through Buffer Overflow attack work?: It typically unfolds over 4 phases. It begins with: [Survey] The attacker surveys the target application, possibly as a valid and authenticated user
How do you prevent CAPEC-24?: 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.
What weaknesses does CAPEC-24 target?: CAPEC-24 exploits 8 CWE weaknesses, including CWE-20 (Improper Input Validation), CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')), CWE-118 (Incorrect Access of Indexable Resource ('Range Error')), CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer).
How severe is CAPEC-24?: MITRE rates CAPEC-24 as High severity with high likelihood of attack.

References

Attack-pattern data is sourced from the MITRE CAPEC catalog (v3.9). Weakness associations link to the corresponding CWE entries on RadicalNotion.AI.

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