Numeric Range Comparison Without Minimum Check

Opis

The product checks a value to ensure that it is less than or equal to a maximum, but it does not also verify that the value is greater than or equal to the minimum.

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.

Inne nazwy

Signed comparison

The "signed comparison" term is often used to describe when the product uses a signed variable and checks it to ensure that it is less than a maximum value (typically a maximum buffer size), but does not verify that it is greater than 0.

Skutki

• Integrity, Confidentiality, Availability

  Modify Application Data; Execute Unauthorized Code or Commands

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

• Availability

  DoS: Resource Consumption (Other)

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

• Confidentiality, Integrity

  Modify Memory; Read 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.

Zapobieganie

• Implementation · Enforcement by Conversion

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

• Implementation · Input Validation

  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.

Przykłady podatności

• CVE-2010-1866 Chain: integer overflow (CWE-190) causes a negative signed value, which later bypasses a maximum-only check (CWE-839), leading to heap-based buffer overflow (CWE-122).
• CVE-2009-1099 Chain: 16-bit counter can be interpreted as a negative value, compared to a 32-bit maximum value, leading to buffer under-write.
• CVE-2011-0521 Chain: kernel's lack of a check for a negative value leads to memory corruption.
• CVE-2010-3704 Chain: parser uses atoi() but does not check for a negative value, which can happen on some platforms, leading to buffer under-write.
• CVE-2010-2530 Chain: Negative value stored in an int bypasses a size check and causes allocation of large amounts of memory.
• CVE-2009-3080 Chain: negative offset value to IOCTL bypasses check for maximum index, then used as an array index for buffer under-read.
• CVE-2008-6393 chain: file transfer client performs signed comparison, leading to integer overflow and heap-based buffer overflow.
• CVE-2008-4558 chain: negative ID in media player bypasses check for maximum index, then used as an array index for buffer under-read.

Słabość nadrzędna

• CWE-1023 Incomplete Comparison with Missing Factors

Może prowadzić do

• CWE-195 Signed to Unsigned Conversion Error
• CWE-682 Incorrect Calculation
• CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer
• CWE-124 Buffer Underwrite ('Buffer Underflow')

Kiedy powstaje

• Implementation

Dotyczy

C, C++

Źródła

1. The Art of Software Security Assessment — Mark Dowd, John McDonald, Justin Schuh, Chapter 6, "Type Conversion Vulnerabilities" Page 246, Addison Wesley, 2006
2. The Art of Software Security Assessment — Mark Dowd, John McDonald, Justin Schuh, Chapter 6, "Comparisons", Page 265, Addison Wesley, 2006