CWE-196

Unsigned to Signed Conversion Error
AI Translation Available

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.

Status
draft
Abstraction
variant
Likelihood
medium
C C++

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.

Common Consequences

availability integrity confidentiality access control
Impacts
dos: crash, exit, or restart modify memory execute unauthorized code or commands bypass protection mechanism

Detection Methods

automated static analysis

Potential Mitigations

Phases:
requirements architecture and design implementation
Descriptions:
• Choose a language which is not subject to these casting flaws.
• Error check the return values of all functions. Be aware of implicit casts made, and use unsigned variables for sizes if at all possible.
• 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.