Improper Validation of Specified Quantity in Input

Description

This vulnerability occurs when an application accepts user input meant to define a quantity—like a number, size, or count—but fails to properly check if that value is safe and reasonable before using it.

Extended Description

Applications constantly handle user-defined quantities: file sizes to upload, lengths for arrays, loop iteration counts, or prices for transactions. If your code trusts these numbers without scrutiny, it can be tricked into performing dangerous actions. Attackers exploit this by submitting extreme or malicious values—like a negative number, an impossibly large size, or zero—to manipulate the program's logic, crash it, or force it into an unstable state. Failing to validate quantities has direct consequences. Your application might allocate all available memory based on a huge size, perform a calculation that leads to an integer overflow, or enter an infinite loop. This opens the door to denial-of-service, buffer overflows, or logic flaws that compromise security. Always treat any user-supplied quantity as untrusted and enforce strict rules for minimums, maximums, and expected ranges before the value is used in any operation.

Common Consequences 1

Scope: Other

Impact: Varies by Context

Since quantities are used so often to affect resource allocation or process financial data, they are often present in many places in the code.

Potential Mitigations 1

Phase: Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

Effectiveness: High

Demonstrative Examples 2

ID : DX-135

This example demonstrates a shopping interaction in which the user is free to specify the quantity of items to be purchased and a total is calculated.

Code Example:Bad
Java
java

The user has no control over the price variable, however the code does not prevent a negative value from being specified for quantity. If an attacker were to provide a negative value, then the user would have their account credited instead of debited.

ID : DX-136

This example asks the user for a height and width of an m X n game board with a maximum dimension of 100 squares.

Code Example:

Bad

/* board dimensions /

While this code checks to make sure the user cannot specify large, positive integers and consume too much memory, it does not check for negative values supplied by the user. As a result, an attacker can perform a resource consumption (Uncontrolled Resource Consumption) attack against this program by specifying two, large negative values that will not overflow, resulting in a very large memory allocation (Memory Allocation with Excessive Size Value) and possibly a system crash. Alternatively, an attacker can provide very large negative values which will cause an integer overflow (Integer Overflow or Wraparound) and unexpected behavior will follow depending on how the values are treated in the remainder of the program.

Observed Examples 3

CVE-2019-19911Chain: Python library does not limit the resources used to process images that specify a very large number of bands (Improper Validation of Specified Quantity in Input), leading to excessive memory consumption (Memory Allocation with Excessive Size Value) or an integer overflow (Integer Overflow or Wraparound).

CVE-2008-1440lack of validation of length field leads to infinite loop

CVE-2008-2374lack of validation of string length fields allows memory consumption or buffer over-read

Applicable Platforms

Languages:

Not Language-Specific : Often

Modes of Introduction

Implementation

Related Weaknesses

ChildOf:

Improper Input Validation (CWE-20)

ChildOf:

Improper Input Validation (CWE-20)

CanPrecede:

Memory Allocation with Excessive Size Value (CWE-789)

Notes

MaintenanceThis entry is still under development and will continue to see updates and content improvements.