CVE CyberSecurity Database News

CVE-2025-21424 - Memory Corruption in NPU Driver API under Concurrent Access

Poster -

In early 2025, a new vulnerability was found in some devices using Neural Processing Unit (NPU) drivers. This weakness was cataloged as CVE-2025-21424. At its core, it allows an attacker to corrupt memory by calling specific NPU driver APIs at the same time from multiple threads or processes. In simple words: attackers can crash a device or potentially run code they shouldn't, just by interacting with the device in a certain way.

This post will break down CVE-2025-21424 so you can understand what happened, how bad it is, and what to do to stay safe.

What is CVE-2025-21424?

CVE-2025-21424 is a vulnerability caused by improper handling of resources inside the NPU (Neural Processing Unit) driver when its APIs are called concurrently (from different threads/processes at the same time). The core problem lies in the driver's internal code that does not safely control access to shared memory or data. As a result, the memory can become corrupted—a classic race condition—which could let attackers crash your system or even run malicious code.

This sort of issue is sometimes called a "time-of-check to time-of-use" (TOCTOU) bug or just a race condition.

How Does the Vulnerability Work?

The NPU driver provides an API that lets apps, frameworks, and sometimes users interact with AI hardware. This API is supposed to be safe even when many apps or threads use it at once. However, with CVE-2025-21424, the API is not thread-safe.

Here’s, in simple terms, how attackers can exploit it

1. Concurrent Calls: An attacker writes a program that calls the NPU driver API many times in parallel (using threads or processes).
2. Race Condition: Because the driver doesn't safely handle these parallel requests, two (or more) calls can edit or read shared data at the same time.

Memory Corruption: This random access leads to heap or stack memory getting corrupted.

4. Impact: Crashing the process, escalating privileges, or executing arbitrary code (depending on memory layout and exploitation skill).

Vulnerable Code Example

While we can’t post the real vendor’s proprietary code, here’s a pseudo code example showing the unsafe logic:

// Pseudo code from inside NPU driver
int resource_in_use = ;

int npu_api_function() {
    if (resource_in_use) {
        return ERROR_BUSY;
    }
    resource_in_use = 1;
    // [critical section: work with shared memory]
    do_npu_work();
    resource_in_use = ;
    return SUCCESS;
}

Now imagine two threads running npu_api_function() at nearly the same time. Both might check resource_in_use before it is set, causing both to enter the critical section together—corrupting memory.

To fix this, programmers use a *mutex* (mutual exclusion lock)

pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;

int npu_api_function() {
    pthread_mutex_lock(&lock);
    do_npu_work();
    pthread_mutex_unlock(&lock);
    return SUCCESS;
}

But in case of CVE-2025-21424, the real driver lacked this safety.

Affected Products

So far, this vulnerability was found in several Android smartphones and AI-powered embedded devices using affected NPU drivers, particularly in chipsets from some major vendors in Asia. Specific device lists can be checked in vendor security advisories, but it is likely other hardware using similar drivers are at risk.

Proof-of-Concept Exploit Code

Here is a simple demo (in C) to trigger the problem. (Note: adapt the API calls for your platform, and *never use exploit code on devices you don’t own!*)

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

#define NUM_THREADS 100

void *thread_func(void *arg) {
    for (int i = ; i < 100; i++) {
        // Replace with real NPU API call
        npu_api_function();
    }
    return NULL;
}

int main() {
    pthread_t threads[NUM_THREADS];
    for (int i = ; i < NUM_THREADS; ++i)
        pthread_create(&threads[i], NULL, thread_func, NULL);
    for (int i = ; i < NUM_THREADS; ++i)
        pthread_join(threads[i], NULL);

    printf("Done\n");
    return ;
}

When run on a vulnerable system, this code can easily crash the driver, the app, or even the kernel.

Exploiting a race condition can be tricky but here is a simple rundown

- Privilege Required: If the NPU API is exposed to user apps (such as Android's HAL), a malicious app can use this bug without special privileges.
- Impact: The worst-case is local code execution inside the hardware abstraction layer, potentially allowing full device compromise.
- Real-World Attacks: So far, no public cases, but the pattern is easy to weaponize for bypassing app sandboxes or gaining higher privileges on a device.

If you think your device *might* be affected

1. Update Your Device: Look for security patches from your device or chipset vendor. If unsure, check the Android Pixel Update Bulletin.
2. Limit App Installs: Don't install untrusted apps, especially those needing hardware/AI access.
3. Restrict NPU Access: System admins can sometimes restrict access to hardware devices until a patch is released.
4. Developers: Make sure to use proper locking (mutex/semaphores) in your device drivers if you design or maintain low-level code!

References

- CVE-2025-21424 at NVD (National Vulnerability Database) *(if available)*
- Android Security Bulletins
- Example of similar race condition bugs: CVE-202-12351 - Bluetooth Race Condition

Summary

CVE-2025-21424 is a dangerous bug in some NPU drivers when APIs are called from multiple threads or processes. It’s easy to exploit and can have major impacts on device and user security. The fix is simple for developers: always use proper locking! For users, apply updates and be cautious with the apps you install.

Timeline

Published on: 03/03/2025 11:15:15 UTC
Last modified on: 03/07/2025 14:12:17 UTC