CWE-194 (未预期的符号扩展) — Vulnerability Class 4

CWE-194 represents a critical logic error where a negative value undergoes sign extension during type conversion to a larger data type, resulting in unintended positive values. This weakness typically arises when developers assume unsigned behavior for signed integers or vice versa, leading to severe security vulnerabilities such as buffer overflows or integer overflows. Attackers exploit this by supplying carefully crafted negative inputs that, upon extension, bypass boundary checks or allocate excessive memory, allowing for arbitrary code execution or denial of service. To prevent this, developers must explicitly cast variables to the correct signed or unsigned types before arithmetic operations, validate input ranges strictly, and utilize static analysis tools to detect implicit conversions. Ensuring consistent type handling and rigorous testing of edge cases involving negative numbers is essential for maintaining application integrity and preventing exploitation of sign extension flaws.