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CAPEC-491:Quadratic Data Expansion

Attack Pattern ID:491

Version:v3.9

Attack Pattern Name:Quadratic Data Expansion

Abstraction:Detailed

Status:Draft

Details Content History Related Weaknesses Reports

▼Description

An adversary exploits macro-like substitution to cause a denial of service situation due to excessive memory being allocated to fully expand the data. The result of this denial of service could cause the application to freeze or crash. This involves defining a very large entity and using it multiple times in a single entity substitution. CAPEC-197 is a similar attack pattern, but it is easier to discover and defend against. This attack pattern does not perform multi-level substitution and therefore does not obviously appear to consume extensive resources.

▼Alternate Terms

XML Entity Expansion (XEE)

▼Relationships

Nature	Type	ID	Name
ChildOf	S	230	Serialized Data with Nested Payloads
CanFollow	D	228	DTD Injection

Nature: ChildOf

Type: Standard

ID: 230

Name: Serialized Data with Nested Payloads

Nature: CanFollow

Type: Detailed

ID: 228

Name: DTD Injection

▼Execution Flow

Explore

Survey the target

An adversary determines the input data stream that is being processed by a data parser that supports using substituion on the victim's side.

Technique
Use an automated tool to record all instances of URLs to process requests.
Use a browser to manually explore the website and analyze how the application processes requests.

Exploit

Craft malicious payload

The adversary crafts malicious message containing nested quadratic expansion that completely uses up available server resource.

Send the message

Send the malicious crafted message to the target URL.

▼Prerequisites

This type of attack requires a server that accepts serialization data which supports substitution and parses the data.

▼Consequences

Scope	Likelihood	Impact	Note
Availability	N/A	Unreliable ExecutionResource Consumption	Denial of Service

Scope: Availability

Likelihood: N/A

Impact: Unreliable Execution, Resource Consumption

Note: Denial of Service

▼Mitigations

Design: Use libraries and templates that minimize unfiltered input. Use methods that limit entity expansion and throw exceptions on attempted entity expansion.

Implementation: For XML based data - disable altogether the use of inline DTD schemas when parsing XML objects. If a DTD must be used, normalize, filter and use an allowlist and parse with methods and routines that will detect entity expansion from untrusted sources.

▼Example Instances

▼Related Weaknesses

ID	Name
CWE-770	Allocation of Resources Without Limits or Throttling

ID: CWE-770

Name: Allocation of Resources Without Limits or Throttling