A JSON parser is software that reads JSON text and converts it into data structures or objects an application can use. In a web service, it sits between an incoming request and the application logic, turning bytes on the wire into fields, arrays, and types the program understands.
That makes parsers security-sensitive. If they process untrusted input, flaws in the parser or in how the application uses it can lead to deserialization bugs, type confusion, denial of service, or even remote code execution. In real attacks, adversaries send crafted JSON to APIs, hoping the parser will accept dangerous values or trigger unsafe object creation before the rest of the application can validate the request. Defenders reduce this risk by keeping parser libraries patched, limiting automatic type binding, using safer parser modes, and treating JSON handling as part of the trust boundary.