A recursive descent parser is a top-down parser built from a chain of functions, where each function recognizes one part of a grammar and may call other functions to parse nested structure. It is common in language tools, configuration parsers, and libraries that turn text into trees or abstract syntax trees.
In cyber security, parsers matter because they sit on the boundary between raw input and trusted logic. A buggy parser can misread attacker-controlled data, leading to crashes, denial of service, infinite recursion, or security checks that are bypassed. Defenders also use recursive descent parsers in code analysis, protocol inspection, and validation tools, where accurate grammar handling helps detect malformed or malicious input. When a project depends on a parsing library, that dependency becomes part of the trust chain, so typosquatted or compromised packages can be especially risky.