An adversary corrupts or modifies the content of a schema for the purpose of undermining the security of the target. Schemas provide the structure and content definitions for resources used by an application. By replacing or modifying a schema, the adversary can affect how the application handles or interprets a resource, often leading to possible denial of service, entering into an unexpected state, or recording incomplete data.

How does a Schema Poisoning attack work?

It typically unfolds over 3 phases. It begins with: [Find target application and schema] The adversary first finds the application that they want to target. This application must use schemas in some way, so the adversary also needs to confirm that schemas are being used.

How do you prevent CAPEC-271?

Design: Protect the schema against unauthorized modification.

What weaknesses does CAPEC-271 target?

CAPEC-271 exploits 1 CWE weakness, including CWE-15 (External Control of System or Configuration Setting).

How severe is CAPEC-271?

MITRE rates CAPEC-271 as High severity with low likelihood of attack.

CAPEC-271: Schema Poisoning

How the attack works

The phases an attacker typically follows to carry out this attack.

Step 1
Explore
[Find target application and schema] The adversary first finds the application that they want to target. This application must use schemas in some way, so the adversary also needs to confirm that schemas are being used.
- Gain access to the system that the application is on and look for a schema.
- Observe HTTP traffic to the application and look for a schema being transmitted.
Step 2
Experiment
[Gain access to schema] The adversary gains access to the schema so that they can modify the contents.
- For a local scenario, the adversary needs access to the machine that the schema is located on and gain permissions to alter the contents of the schema file.
- For a remote scenario, the adversary needs to be able to perform an adversary in the middle attack on the HTTP traffic that contains a schema.
Step 3
Exploit
[Poison schema] Once the adversary gains access to the schema, they will alter it to achieve a desired effect. Locally, they can just modify the file. For remote schemas, the adversary will alter the schema in transit by performing an adversary in the middle attack.
- Cause a denial of service by modifying the schema so that it does not contain required information for subsequent processing.
- Manipulation of the data types described in the schema may affect the results of calculations. For example, a float field could be changed to an int field.
- Change the encoding defined in the schema for certain fields allowing the contents to bypass filters that scan for dangerous strings. For example, the modified schema might use a URL encoding instead of ASCII, and a filter that catches a semicolon (;) might fail to detect its URL encoding (%3B).

How the attack works

CAPEC-271: Schema Poisoning

Overview

How the attack works

What the attacker needs

Prerequisites

Resources required

Consequences

How to mitigate it

Examples

Frequently asked questions

What is CAPEC-271?

How does a Schema Poisoning attack work?

How do you prevent CAPEC-271?

What weaknesses does CAPEC-271 target?

How severe is CAPEC-271?

References

Defend against CAPEC-271

How the attack works

Overview

How the attack works

What the attacker needs

Prerequisites

Resources required

Consequences

How to mitigate it

Examples

Related weaknesses

Related attack patterns

Parent

Child

Can follow

Frequently asked questions

What is CAPEC-271?

How does a Schema Poisoning attack work?

How do you prevent CAPEC-271?

What weaknesses does CAPEC-271 target?

How severe is CAPEC-271?

References

Defend against CAPEC-271