The CWE-190 vulnerability mentioned refers to an "Integer Overflow or Wraparound." This type of vulnerability occurs when an integer operation results in a value that is outside the range that can be represented with a given number of bits. In the context of the provided code, the vulnerability at line 108 is likely due to the subtraction operation on `smh->submessageLength`.

Here's a breakdown of the issue:

1. **Subtraction without validation**: At line 108, the code performs a subtraction operation on `smh->submessageLength` without ensuring that the value being subtracted is less than or equal to `smh->submessageLength`. This can lead to an integer underflow.

2. **Type and Range of `smh->submessageLength`**: The type of `smh->submessageLength` is not explicitly mentioned, but it is likely an unsigned integer type based on typical usage patterns in similar contexts. If `smh->submessageLength` is an unsigned integer, subtracting a larger value from it will cause an underflow, wrapping around to a very large value.

3. **Potential Impact of Underflow**: If `payload_size` underflows and becomes a very large number, subsequent operations that use `payload_size` (such as memory allocation, buffer size calculations, or array indexing) could behave incorrectly, leading to buffer overflows, incorrect processing, or crashes.

4. **Lack of Boundary Checks**: Before performing the subtraction, the code does not check whether the value being subtracted (which is not shown in the provided code snippet but is implied to be part of the calculation) is less than or equal to `smh->submessageLength`. This lack of boundary checking leads directly to the vulnerability.

To mitigate this vulnerability, the code should include checks to ensure that the value being subtracted is not greater than `smh->submessageLength`. For example:
```cpp
if (value_to_subtract > smh->submessageLength) {
    // Handle error: underflow condition
} else {
    payload_size = smh->submessageLength - value_to_subtract;
}
```
This check prevents the underflow by ensuring that the subtraction only occurs when it is safe to do so, thereby maintaining the integrity of `payload_size`.

Additionally, it's crucial to validate all external inputs and data from untrusted sources to ensure they meet expected ranges and constraints before using them in calculations or operations that could affect program stability or security.