CWE-196: Unsigned to Signed Conversion Error
Description
The product uses an unsigned primitive and performs a cast to a signed primitive, which can produce an unexpected value if the value of the unsigned primitive can not be represented using a signed primitive.
Although less frequent an issue than signed-to-unsigned conversion, unsigned-to-signed conversion can be the perfect precursor to dangerous buffer underwrite conditions that allow attackers to move down the stack where they otherwise might not have access in a normal buffer overflow condition. Buffer underwrites occur frequently when large unsigned values are cast to signed values, and then used as indexes into a buffer or for pointer arithmetic.
- Abstraction
- VariantA weakness tied to a specific language, technology or resource.
- Likelihood of exploit
- Medium
- Status
- Draft
Common consequences
- Availability
DoS: Crash, Exit, or Restart
Incorrect sign conversions generally lead to undefined behavior, and therefore crashes.
- Integrity
Modify Memory
If a poor cast lead to a buffer overflow or similar condition, data integrity may be affected.
- IntegrityConfidentialityAvailabilityAccess Control
Execute Unauthorized Code or Commands; Bypass Protection Mechanism
Improper signed-to-unsigned conversions without proper checking can sometimes trigger buffer overflows which can be used to execute arbitrary code. This is usually outside the scope of a program's implicit security policy.
Potential mitigations
- Requirements
Choose a language which is not subject to these casting flaws.
- Architecture and Design
Design object accessor functions to implicitly check values for valid sizes. Ensure that all functions which will be used as a size are checked previous to use as a size. If the language permits, throw exceptions rather than using in-band errors.
- Implementation
Error check the return values of all functions. Be aware of implicit casts made, and use unsigned variables for sizes if at all possible.