In June 2022, security researchers revealed CVE-2022-32612, a use-after-free vulnerability resulting from a race condition in MediaTek's VCU (Video Codec Unit) driver. This flaw could allow a local attacker to escalate privileges to the system level, and it is exploitable without user interaction. In this deep dive, we'll break down how the bug occurs, step through a simplified proof-of-concept, and provide mitigation information. Let's start from the beginning!

What Is CVE-2022-32612?

CVE-2022-32612 is a vulnerability in the VCU driver typically found on MediaTek-powered smartphones and devices. The VCU handles decoding and encoding videos — a critical part of the multimedia pipeline. The vulnerability is triggered by a race condition, which leads to a use-after-free (UAF): one part of the code frees a structure while another still has a reference to it. As a result, an attacker could control what gets put in the freed memory, and trick the system into executing code with higher privileges.

Race Condition? Use-After-Free? Plain English, Please!

A race condition happens when two processes or threads try to access and change data at the same time, and the program doesn’t handle these perfectly timed events.

A use-after-free occurs when a program uses memory after it has already been freed (released back to the system). Normally, after you free memory, you shouldn't access it anymore. If you do, and if an attacker can control the freed memory, bad things can happen!

How Does This Affect the VCU?

In the VCU implementation, two threads can work with the same memory structure. One thread may free the memory, while the other is still depending on it. This opens the door for an attacker to perform "heap spraying" — filling memory with their own data in hopes the freed spot will now point to their payload.

Imagine a very simplified version of the code

// Pseudocode inspired by mediaserver handling VCU structures

// Thread 1: Free
void thread1_cleanup(struct vcu_work *work) {
    free(work);
}

// Thread 2: Use
void thread2_process(struct vcu_work *work) {
    // Assume no locking in place
    process(work->data); // UAF if work is freed by thread1
}

Without the proper locks, it's possible work is freed in thread1 while thread2 is still working with it.

Attack Strategy

1. Trigger the race: The attacker repeatedly triggers VCU operations, creating new session requests and rapidly destroying them, hoping to hit the race window.
2. Heap spraying: While deallocation and reallocation are in a tight loop, attacker sprays the heap with their custom payload, placing it where the VCU structure gets re-used.
3. Hijack flow: When the driver tries to process the now-freed pointer, it instead uses attacker-controlled memory, potentially leading to privilege escalation and SYSTEM-level access.

A (Simplified) Proof-of-Concept

Below is a pseudocode (C language) approximation demonstrating the favored attack scenario. This is meant for educational purposes only!

// Simplified PoC: WARNING! DO NOT RUN ON UNPATCHED DEVICES!

int main() {
    int i;

    // 1. Spray heap with attack data
    for (i = ; i < SPRAY_COUNT; i++) {
        spray_heap_with_fake_vcu_struct(i);
    }

    // 2. Launch multiple threads to trigger race
    pthread_t t1, t2;
    struct vcu_work *work = allocate_real_vcu_struct();

    pthread_create(&t1, NULL, (void *)thread1_cleanup, work);
    pthread_create(&t2, NULL, (void *)thread2_process, work);

    pthread_join(t1, NULL);
    pthread_join(t2, NULL);

    // If exploit successful, SYSTEM privileges are gained.
}

Note: The real exploit would be more complex and device-specific, but this is the basic logic.

Patch and Mitigation

MediaTek fixed the bug in their patch ALPS07203500. Proper synchronization (locks/mutexes) are now used to prevent the UAF situation during VCU operations.

What You Should Do

- Update your device: Make sure your MediaTek device has the latest firmware/security patch from your OEM (check for security bulletins dated after mid-2022).
- Watch for device recalls or firmware news: If your phone isn’t patched, consider contacting support.

Official MediaTek Security Advisory:

https://www.mediatek.com/security-bulletins

NIST NVD Entry for CVE-2022-32612:

https://nvd.nist.gov/vuln/detail/CVE-2022-32612

Google Android Security Bulletin, June 2022:

https://source.android.com/docs/security/bulletin/2022-06-01

Final Thoughts

CVE-2022-32612 illustrates why robust synchronization is needed in kernel and driver code, especially when dealing with user-accessible interfaces on millions of smartphones. If you use a MediaTek device (especially older or mid-range models), make sure you’re running up-to-date firmware. Don't ignore those system updates — they patch serious problems like this before attackers can get SYSTEM-level access!

Timeline

Published on: 11/08/2022 21:15:00 UTC
Last modified on: 11/10/2022 13:41:00 UTC