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Resolve vulnerability: Divide a number by zero

Igor Drozdovrequested to merge
remediate/divide-a-number-by-zero-D20250318T093613 into main

MR created from vulnerability: Divide a number by zero

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Description:

A ZeroDivisionError exception has been detected, this occurs when an arithmetic operation attempts to divide a number by zero. This can happen in various contexts, such as processing user inputs, performing calculations with variables, or working with data from external sources. Such errors not only disrupt the normal flow of the application but also can be exploited in certain scenarios to cause harm (eg. possible dos) or extract information based on the application's response to the error.

To prevent ZeroDivisionError exceptions and ensure application robustness:

  • Error handling: Implement error handling around division operations to catch and manage ZeroDivisionError gracefully.
  • Validation: Always validate inputs that are used in division operations to ensure they are not zero or unexpected values.

Analysis:

The vulnerability report indicates a potential "Divide by Zero" issue, which is classified under CWE-369. This type of vulnerability can lead to runtime errors, application crashes, or unexpected behavior.

The specific part of the code flagged as vulnerable is:

z = x / y # warns

This line is part of the divide_by_zero method in the JustAClass class. The potential security implication is that if y becomes zero, it will cause a divide by zero error, which could crash the application or lead to unexpected behavior.

The context shows that y is calculated as x - 100, where x is set to 100. This means that y will always be 0, guaranteeing a divide by zero error when z = x / y is executed.

This is a genuine security concern as it can lead to application instability and potential denial of service if exploited.

Summary:

  1. The reported vulnerability is a potential "Divide by Zero" issue (CWE-369) in the divide_by_zero method of the JustAClass class.

  2. The fix provided addresses the security concern by adding a check for zero before performing the division operation:

z = y.zero? ? nil : x / y

This change prevents the divide by zero error by returning nil when y is zero. This approach maintains the overall functionality while avoiding the runtime error.

  1. It's important to note that the other division operations in the method (whatever / 0 and 1.0 / 0) were left unchanged but should be reviewed as they also represent potential divide by zero issues. The 1.0 / 0 operation doesn't trigger a warning because it results in Infinity in Ruby, which is a valid floating-point value, but it may not be the intended behavior.

  2. For a more comprehensive fix, the entire divide_by_zero method should be reviewed and potentially refactored to remove or properly handle all instances of division that could result in a divide by zero error.

  3. Additionally, it's recommended to add error handling and logging mechanisms to capture and report any unexpected zero divisor situations, which could help in identifying and addressing potential issues in the future.

Identifiers:

  • CWE-369
  • A6:2017 - Security Misconfiguration
  • Brakeman Warning Code 104
  • brakeman.ruby_error_rule-DivideByZero
  • A04:2021 - Insecure Design

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