System Crash Caused by uint8 Overflow: Real Case Analysis and Prevention Strategies

# 1. Overview of uint8 Overflow

**uint8 Data Type**

The uint8 data type is an 8-bit unsigned integer, ranging from 0 to 255. It is widely used to store small integers such as counters, flags, and status values.

**Overflow**

Overflow occurs when the result of an arithmetic operation on a uint8 variable exceeds its range (0~255). When an overflow happens, the result wraps around to the other end of the range. For example, if you add 1 to a uint8 variable with the value 255, the result becomes 0 due to the overflow.

# 2. The Mechanism of System Crashes Caused by uint8 Overflow

### 2.1 Characteristics and Limitations of uint8 Data Type

The uint8 is an 8-bit unsigned integer data type with a value range of 0 to 255. Unlike signed integers, uint8 cannot represent negative numbers, limiting its applications in certain scenarios.

### 2.2 Causes and Impacts of Overflow

Overflow happens when the value of a uint8 variable exceeds its value range. There are two types of overflows:

- **Positive Overflow:** When the value of a uint8 variable exceeds 255, it starts counting from 0 again. For example, if the value of uint8 variable x is 255 and is incremented by 1, the value of x becomes 0 due to positive overflow.
- **Negative Overflow:** When the value of a uint8 variable is less than 0, it starts counting from 255 again. For example, if the value of uint8 variable x is 0 and is decremented by 1, the value of x becomes 255 due to negative overflow.

The reasons for system crashes caused by overflow include:

- **Data Error:** After an overflow, the value of the uint8 variable no longer represents its intended value, leading to data errors.
- **Program Logic Disruption:** Data errors from an overflow can disrupt program logic, causing abnormal program execution.
- **Memory Corruption:** In some cases, overflow may lead to memory corruption, resulting in system crashes.

### Code Example

The following code example demonstrates uint8 overflow:

uint8_t x = 255;
x++; // Positive overflow, x becomes 0

### Logical Analysis

In this code example, the value of the uint8 variable x is 255, and after incrementing by 1, the value of x overflows and becomes 0. This is because the uint8 data type can only represent values between 0 and 255, and overflowing this range will cause overflow.

### Parameter Description

- **uint8_t:** Unsigned 8-bit integer data type
- **x:** uint8 variable

# 3. Real-Case Analysis

### 3.1 Discovery and Replication of the Vulnerability

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