CWE-194 Unexpected Sign Extension

The product performs an operation on a number that causes it to be sign extended when it is transformed into a larger data type.

• Integrity, Confidentiality, Availability, Other: Read Memory, Modify Memory, Other — When an unexpected sign extension occurs in code that operates directly on memory buffers, such as a size value or a memory index, then it could cause the program to write or read outside the boundaries of the intended buffer. If the numeric value is associated with an application-level resource, such as a quantity or price for a product in an e-commerce site, then the sign extension could produce a value that is much higher (or lower) than the application's allowable range. When the original number is negative, this can produce unexpected values that lead to resultant weaknesses.

• [Implementation] Avoid using signed variables if you don't need to represent negative values. When negative values are needed, perform validation after you save those values to larger data types, or before passing them to functions that are expecting unsigned values.

• Automated Static Analysis: Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

• CVE-2018-10887: Chain: unexpected sign extension (CWE-194) leads to integer overflow (CWE-190), causing an out-of-bounds read (CWE-125) • CVE-1999-0234: Sign extension error produces -1 value that is treated as a command separator, enabling OS command injection. • CVE-2003-0161: Product uses "char" type for input character. When char is implemented as a signed type, ASCII value 0xFF (255), a sign extension produces a -1 value that is treated as a program-specific separator value, effectively disabling a length check and leading to a buffer overflow. This is also a multiple interpretation error. • CVE-2007-4988: Chain: signed short width value in image processor is sign extended during conversion to unsigned int, which leads to integer overflow and heap-based buffer overflow. • CVE-2006-1834: Chain: signedness error allows bypass of a length check; later sign extension makes exploitation easier. • CVE-2005-2753: Sign extension when manipulating Pascal-style strings leads to integer overflow and improper memory copy.