A parsing flaw is a bug in code that reads and interprets structured input such as JSON, XML, command-line arguments, connection strings, or database queries. The parser may misread fields, accept malformed data, convert values incorrectly, or stop processing in an unexpected state. Even small mistakes can lead to crashes, corrupted data, or security checks being skipped.
In cyber security, parsing flaws matter because attackers often supply the input that a parser handles. If untrusted data reaches a vulnerable parser, it may trigger denial of service, enable injection, or bypass validation and access controls. Defenders look for these bugs in client libraries, admin tools, framework glue, and file import features, where data is transformed before it reaches a server or business logic. Secure parsing requires strict input validation, safe type conversion, clear error handling, and patching libraries that process external data.