We all know that security vulnerabilities can compromise the integrity of a system, potentially leading to a loss of confidentiality and unauthorized access. CVE-2018-9387, a particularly significant vulnerability, has caught our attention. This post will dissect this vulnerability, which affects multiple functions of the mnh-sm.c file, and can trigger a heap overflow due to an integer overflow. This allows an attacker to perform local escalation of privilege with no additional execution privileges needed. Additionally, user interaction is not required for the exploitation of this vulnerability. We will dive deep into the technical details, exploring code snippets, links to original references, and detailing the exploit involved.

The Vulnerability: Heap Overflow due to Integer Overflow

In multiple functions of the mnh-sm.c file, a critical vulnerability exists, allowing an attacker to trigger a heap overflow using an integer overflow. For those unfamiliar with the concept, a heap overflow is a type of buffer overflow, occurring when a program writes more data into a block of memory (heap) than it was initially allocated. This can cause a corruption in the data and allow an attacker to gain control over the system.

In this specific case, CVE-2018-9387 makes use of an integer overflow, which occurs when an integer value surpasses the maximum limit of the data type, causing it to wrap around and result in a smaller, incorrect value. This can lead to a heap overflow, as we will see in the following sections.

Code Snippet

/* mnh-sm.c */

int parse_data(char *data, int data_size) {
    int num_elements;
    unsigned int i;
    unsigned int alloc_size;

    num_elements = ;
    for (i = ; i < data_size;) {
        num_elements++;
        i += data[i];
    }

    /* Integer overflow occurs here */
    alloc_size = num_elements * sizeof(element);
    element *elements = (element *)malloc(alloc_size);

    /* Heap overflow occurs here */
    int j = ;
    for (i = ; i < data_size;) {
        elements[j].size = data[i];
        memcpy(elements[j].elem, &data[i+1], elements[j].size);

        i += data[i];
        j++;
    }

    return ;
}

In the code snippet above, the variable num_elements is incremented inside the loop, which can lead to a large value that multiplies the size of an element. This causes an integer overflow in the alloc_size variable. During the memory allocation with malloc, a smaller amount of memory will be assigned to the pointer elements. Subsequently, the memory copying in the next loop will lead to a heap overflow due to the mismatch of allocated memory and data size.

Exploit Details

As mentioned earlier, this vulnerability does not require user interaction nor additional execution privileges for exploitation. The attacker can craft a specific input data that triggers the integer overflow and eventually leads to a heap overflow. By carefully controlling the input data size and element sizes, the attacker can cause a memory corruption that allows the execution of arbitrary code.

Original References

1. CVE-2018-9387 entry on NVD (National Vulnerability Database): https://nvd.nist.gov/vuln/detail/CVE-2018-9387
2. Google Android Security Bulletin: https://source.android.com/security/bulletin/2018-08-01

Conclusion

In summary, CVE-2018-9387 is a dangerous vulnerability that affects multiple functions of the mnh-sm.c file. By exploiting an integer overflow, the vulnerability can trigger a heap overflow, potentially allowing an attacker to gain control over the system and escalate privileges. It's crucial to keep systems updated with the latest security patches and be aware of such vulnerabilities to ensure the safety and integrity of your systems.

Timeline

Published on: 01/18/2025 00:15:23 UTC
Last modified on: 03/14/2025 16:15:26 UTC