CWE-196—Unsigned to Signed Conversion Error

Weakness Name

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.

Common Consequences

Scope:

Availability

Impact:

DoS: Crash, Exit, or Restart

Notes:

Incorrect sign conversions generally lead to undefined behavior, and therefore crashes.

Scope:

Integrity

Impact:

Modify Memory

Notes:

If a poor cast lead to a buffer overflow or similar condition, data integrity may be affected.

Scope:

Integrity, Confidentiality, Availability, Access Control

Impact:

Execute Unauthorized Code or Commands, Bypass Protection Mechanism

Notes:

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.

Related Weaknesses

• CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')High
• CWE-124Buffer Underwrite ('Buffer Underflow')Medium
• CWE-681Incorrect Conversion between Numeric TypesHigh