4.1. Threat Model🔗

YAML parsers face several categories of attack:

• Billion-laugh attacks — deeply nested aliases that expand exponentially, exhausting memory

• Denial of service — extremely long strings, deeply nested structures, or very large collections that consume excessive resources

• Arbitrary code execution — YAML tags that trigger object deserialization in languages with unsafe constructors (e.g., Python's !!python/object)

• Duplicate key confusion — multiple identical keys in a mapping, where different consumers may pick different values

L4YAML mitigates all of these through its ParserLimits configuration.