Incorrect Calculation

Opis

The product performs a calculation that generates incorrect or unintended results that are later used in security-critical decisions or resource management.

When product performs a security-critical calculation incorrectly, it might lead to incorrect resource allocations, incorrect privilege assignments, or failed comparisons among other things. Many of the direct results of an incorrect calculation can lead to even larger problems such as failed protection mechanisms or even arbitrary code execution.

Skutki

• Availability

  DoS: Crash, Exit, or Restart

  If the incorrect calculation causes the program to move into an unexpected state, it may lead to a crash or impairment of service.

• Integrity, Confidentiality, Availability

  DoS: Crash, Exit, or Restart; DoS: Resource Consumption (Other); Execute Unauthorized Code or Commands

  If the incorrect calculation is used in the context of resource allocation, it could lead to an out-of-bounds operation (CWE-119) leading to a crash or even arbitrary code execution. Alternatively, it may result in an integer overflow (CWE-190) and / or a resource consumption problem (CWE-400).

• Access Control

  Gain Privileges or Assume Identity

  In the context of privilege or permissions assignment, an incorrect calculation can provide an attacker with access to sensitive resources.

• Access Control

  Bypass Protection Mechanism

  If the incorrect calculation leads to an insufficient comparison (CWE-697), it may compromise a protection mechanism such as a validation routine and allow an attacker to bypass the security-critical code.

Zapobieganie

• Implementation

  Understand your programming language's underlying representation and how it interacts with numeric calculation. Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, "not-a-number" calculations, and how your language handles numbers that are too large or too small for its underlying representation.

• Implementation · Input Validation

  Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.

• Implementation

  Use the appropriate type for the desired action. For example, in C/C++, only use unsigned types for values that could never be negative, such as height, width, or other numbers related to quantity.

• Architecture and Design · Language Selection

  Use languages, libraries, or frameworks that make it easier to handle numbers without unexpected consequences.

  Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++).

• Architecture and Design · Libraries or Frameworks

  Use languages, libraries, or frameworks that make it easier to handle numbers without unexpected consequences.

  Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++).

• Implementation · Compilation or Build Hardening

  Examine compiler warnings closely and eliminate problems with potential security implications, such as signed / unsigned mismatch in memory operations, or use of uninitialized variables. Even if the weakness is rarely exploitable, a single failure may lead to the compromise of the entire system.

Przykłady podatności

• CVE-2020-0022 chain: mobile phone Bluetooth implementation does not include offset when calculating packet length (CWE-682), leading to out-of-bounds write (CWE-787)
• CVE-2010-1378 Chain: incorrect calculation (CWE-682) allows attackers to bypass certificate checks (CWE-295)
• CVE-2004-1363 substitution overflow: buffer overflow using environment variables that are expanded after the length check is performed

Może prowadzić do

• CWE-170 Improper Null Termination

Słabości podrzędne

• CWE-128 Wrap-around Error
• CWE-131 Incorrect Calculation of Buffer Size
• CWE-135 Incorrect Calculation of Multi-Byte String Length
• CWE-190 Integer Overflow or Wraparound
• CWE-191 Integer Underflow (Wrap or Wraparound)
• CWE-193 Off-by-one Error
• CWE-369 Divide By Zero
• CWE-468 Incorrect Pointer Scaling
• CWE-469 Use of Pointer Subtraction to Determine Size
• CWE-1335 Incorrect Bitwise Shift of Integer
• CWE-1339 Insufficient Precision or Accuracy of a Real Number

Kiedy powstaje

• Implementation

Dotyczy

Not Language-Specific, Not Technology-Specific

Uwagi

Weaknesses related to this Pillar appear to be under-studied, especially with respect to classification schemes. Input from academic and other communities could help identify and resolve gaps or organizational difficulties within CWE.

Źródła

1. SafeInt — David LeBlanc, Niels Dekker
2. 24 Deadly Sins of Software Security — Michael Howard, David LeBlanc, John Viega, "Sin 7: Integer Overflows." Page 119, McGraw-Hill, 2010
3. The Art of Software Security Assessment — Mark Dowd, John McDonald, Justin Schuh, Chapter 6, "Signed Integer Boundaries", Page 220, Addison Wesley, 2006