CWE-839

Extended description

Some products use signed integers or floats even when their values are only expected to be positive or 0. An input validation check might assume that the value is positive, and only check for the maximum value. If the value is negative, but the code assumes that the value is positive, this can produce an error. The error may have security consequences if the negative value is used for memory allocation, array access, buffer access, etc. Ultimately, the error could lead to a buffer overflow or other type of memory corruption. The use of a negative number in a positive-only context could have security implications for other types of resources. For example, a shopping cart might check that the user is not requesting more than 10 items, but a request for -3 items could cause the application to calculate a negative price and credit the attacker's account.

Common consequences3

• IntegrityConfidentialityAvailabilityModify Application DataExecute Unauthorized Code or Commands

  An attacker could modify the structure of the message or data being sent to the downstream component, possibly injecting commands.

• AvailabilityDoS: Resource Consumption (Other)

  in some contexts, a negative value could lead to resource consumption.

• ConfidentialityIntegrityModify MemoryRead Memory

  If a negative value is used to access memory, buffers, or other indexable structures, it could access memory outside the bounds of the buffer.

Potential mitigations2

1. Implementation

   If the number to be used is always expected to be positive, change the variable type from signed to unsigned or size_t.

2. Implementation

   If the number to be used could have a negative value based on the specification (thus requiring a signed value), but the number should only be positive to preserve code correctness, then include a check to ensure that the value is positive.

Relationships5

• ChildOfCWE-1023
• CanPrecedeCWE-195
• CanPrecedeCWE-682
• CanPrecedeCWE-119
• CanPrecedeCWE-124