CWE-196 — Unsigned to Signed Conversion Error
CWE-196: Unsigned to Signed Conversion Error
MITRE CWE weakness
| Kind | Weakness |
| Abstraction | Variant |
| Status | Draft |
| Likelihood of exploit | Medium |
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.
Common consequences
- Availability: DoS: Crash, Exit, or Restart
- Integrity: Modify Memory
- Integrity, Confidentiality, Availability, Access Control: Execute Unauthorized Code or Commands, Bypass Protection Mechanism
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.
References
- CWE page: https://cwe.mitre.org/data/definitions/196.html
- CWE list: https://cwe.mitre.org/data/index.html