CAPEC-71

Detailed Abstraction Level
Meta — Very abstract, high-level category
Standard — Specific enough to understand
Detailed — Tied to specific technique Draft MITRE CAPEC Status
Stable — Fully reviewed and complete
Draft — Under development
Incomplete — Partially defined
Deprecated — No longer recommended
Obsolete — Replaced by another CAPEC Likelihood: Medium Severity: High
Using Unicode Encoding to Bypass Validation Logic

Description

An attacker may provide a Unicode string to a system component that is not Unicode aware and use that to circumvent the filter or cause the classifying mechanism to fail to properly understanding the request. That may allow the attacker to slip malicious data past the content filter and/or possibly cause the application to route the request incorrectly.

Prerequisites

Filtering is performed on data that has not be properly canonicalized.

Mitigations

Ensure that the system is Unicode aware and can properly process Unicode data. Do not make an assumption that data will be in ASCII.

Ensure that filtering or input validation is applied to canonical data.

Assume all input is malicious. Create an allowlist that defines all valid input to the software system based on the requirements specifications. Input that does not match against the allowlist should not be permitted to enter into the system.

Skills Required

[Medium] An attacker needs to understand Unicode encodings and have an idea (or be able to find out) what system components may not be Unicode aware.