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Difficulty: HardApplication and Software Vulnerabilities

During a security assessment of a C-based binary processing service, an engineer analyzes the following code snippet responsible for dynamic memory allocation:

`unsigned int total_size = header_size + payload_size;`
`char *buffer = (char *)malloc(total_size);`
`memcpy(buffer, header_data, header_size);`
`memcpy(buffer + header_size, payload_data, payload_size);`

During testing, an input with header_size=0xFFFFFFFFheader\_size = 0xFFFFFFFF (4,294,967,2954,294,967,295) and payload_size=0x00000010payload\_size = 0x00000010 (1616) causes the `total_size` variable to wrap around to 0x0000000F0x0000000F (1515 bytes). As a result, `malloc` allocates a 1515-byte buffer on the heap, but subsequent `memcpy` operations attempt to copy over 44 gigabytes of data into that buffer.

Which of the following vulnerability types is demonstrated by this flaw, and which control best prevents its exploitation?

  1. Integer overflow leading to a heap-based buffer overflow; mitigate by implementing explicit range checking on arithmetic operations before allocating memory.Answer
  2. B
    Cross-site scripting (XSS); mitigate by enforcing contextual HTML entity encoding on all user inputs.
  3. C
    Broken object level authorization; mitigate by validating user session tokens against access control lists prior to processing file headers.
  4. D
    Uncontrolled resource consumption; mitigate by deploying a network-level stateful firewall to block excessive payload requests.

Answer

The correct option identifies the vulnerability as an integer overflow leading to a heap-based buffer overflow, which is mitigated by implementing bounds and range checking on arithmetic operations prior to memory allocation.
The scenario describes an integer overflow where combining two integer values wraps around to a small number due to standard integer storage limits. Because `malloc` uses this wrapped value (1515 bytes), the subsequent copy of the full payload writes memory beyond the allocated buffer boundaries, creating a heap-based buffer overflow. The correct remediation is to validate that arithmetic additions do not overflow before attempting memory allocation.

Step-by-Step Solution

1
Analyze the arithmetic operation in the memory allocation logic.
Adding two 32-bit unsigned integers (0xFFFFFFFF+0x100xFFFFFFFF + 0x10) exceeds the maximum 32-bit integer limit (0xFFFFFFFF0xFFFFFFFF), causing the value to wrap around to 0x0000000F0x0000000F (1515).
This arithmetic wrap-around is a classic integer overflow.
2
Evaluate the impact on memory management routines.
The `malloc` call receives 1515 bytes as its argument, allocating a small memory region on the heap, while `memcpy` attempts to write far more data than allocated.
Writing past the boundaries of an undersized heap allocation results in a heap-based buffer overflow.
3
Determine the appropriate remediation control.
Perform sanity checks (e.g., checking if `UINT_MAX - header_size < payload_size`) before performing addition and memory allocation.
Explicit arithmetic range checking prevents integer wrap-around before `malloc` is executed.

Key Concept

Integer Overflow and Buffer Overflow Vulnerabilities
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Topics

Application and Software Vulnerabilities

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