CAPEC-197: Exponential Data Expansion
Description
An adversary submits data to a target application which contains nested exponential data expansion to produce excessively large output. Many data format languages allow the definition of macro-like structures that can be used to simplify the creation of complex structures. However, this capability can be abused to create excessive demands on a processor's CPU and memory. A small number of nested expansions can result in an exponential growth in demands on memory.
- Likelihood of attack
- High
- Typical severity
- Medium
- Abstraction
- DetailedA low-level, detailed pattern, often for a particular technology.
Mechanism of attack: Abuse Existing Functionality
Prerequisites
- This type of attack requires that the target must receive input but either fail to provide an upper limit for entity expansion or provide a limit that is so large that it does not preclude significant resource consumption.
Skills required
- LowAbility to craft nested data expansion messages.
Consequences
- Availability
Unreliable Execution; Resource Consumption
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.