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Difficulty: Very hardApplication and Software Vulnerabilities

A security analyst is auditing a C-based backend service responsible for processing batch user updates. Code analysis reveals that the buffer allocation calculation `total_bytes = user_count * sizeof(user_record_t)` uses an unsigned 32-bit integer. When a caller supplies a very large `user_count`, the multiplication arithmetic wraps around, resulting in a small memory allocation from `malloc()`. The application then attempts to copy all incoming user records into this undersized buffer, causing arbitrary memory corruption. Which of the following software vulnerabilities is demonstrated in this scenario?

  1. Integer overflow resulting in a heap-based buffer overflowAnswer
  2. B
    Cross-site scripting (XSS) resulting in DOM-based script injection
  3. C
    Broken object level authorization resulting in privilege escalation
  4. D
    Implementation of web application firewalls to block malformed packet headers

Answer

Integer overflow resulting in a heap-based buffer overflow
The scenario describes an arithmetic integer overflow where a calculated memory allocation size exceeds the maximum integer capacity and wraps around to a small value. Passing this reduced value to memory allocation functions causes insufficient memory to be reserved. When the program subsequently writes the entire payload into this undersized allocation, it overwrites adjacent heap memory, leading to a heap-based buffer overflow.

Step-by-Step Solution

1
Analyze the arithmetic operation
The calculation `user_count * sizeof(user_record_t)` exceeds the maximum capacity of a 32-bit unsigned integer.
When an integer variable exceeds its maximum value boundary, it wraps around to a small number near zero.
2
Evaluate memory allocation impact
`malloc()` allocates a small memory buffer based on the wrapped integer value.
The memory allocator receives the smaller, wrapped size argument rather than the actual required storage size.
3
Trace memory copy behavior
Writing all input records into the undersized heap buffer overwrites adjacent heap memory.
The copying routine uses the actual `user_count` instead of checking against the newly allocated buffer size, triggering a heap overflow.

Key Concept

Integer Overflow and Buffer Overflow Vulnerabilities
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Topics

Application and Software Vulnerabilities

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