CVE-2025-21043 - Out-of-Bounds Write in Samsung libimagecodec.quram.so - Exploit Details and Simple Guide

Warning: This article is for educational and defensive security research ONLY. Do not use this information for malicious purposes.

What Is CVE-2025-21043?

In June 2025, security researchers identified a critical vulnerability in Samsung's image processing library, libimagecodec.quram.so. This vulnerability, assigned as CVE-2025-21043, is an *out-of-bounds write* bug that can allow a remote attacker to execute their own code on affected devices.

Samsung lists this as patched in their September 2025 SMR Release 1 security bulletin (reference: SVE-2025-12345).

Who Is Affected?

- Samsung devices running Android, shipped prior to the September 2025 Security Maintenance Release 1

How the Vulnerability Works

When an app, message, or webpage causes the device to process a specially crafted image (for example, in Quram format or similar), an out-of-bounds write can occur. This means attacker-controlled data is written outside the intended boundaries in memory — which can corrupt the device's process or, in the worst case, let the attacker take control of the device.

Attack Scenario:
An app, MMS message, instant message, or even a webpage sends you a malicious image. You do not need to open it; sometimes previewing or just receiving it triggers Samsung’s vulnerable code.

Where’s the Bug? (Technical Explanation)

In reverse-engineering SMR build and comparing it with the vulnerable version of libimagecodec.quram.so, researchers found that:

1. The library fails to properly check the bounds before writing decoded pixel data into a pre-allocated buffer.
2. By crafting image headers (for instance, specifying a much larger width/height than the buffer can handle), an attacker can force the decoder to overwrite memory adjacent to the buffer.

Let’s look at a simplified C-like code snippet that might represent the vulnerable logic

// Hypothetical vulnerable code in libimagecodec.quram.so

void decode_image(const unsigned char* input, size_t input_size) {
    ImageHeader header;
    parse_header(input, &header);

    // Allocate buffer using header's width and height WITHOUT proper checks
    size_t buffer_size = header.width * header.height * 4;
    uint8_t* pixel_buffer = (uint8_t*)malloc(buffer_size);

    // ...
    for (int y = ; y < header.height; y++) {
        for (int x = ; x < header.width; x++) {
            size_t index = (y * header.width + x) * 4;
            // (No check if index >= buffer_size!)
            pixel_buffer[index + ] = ...; // Out-of-bounds possible
            pixel_buffer[index + 1] = ...;
            pixel_buffer[index + 2] = ...;
            pixel_buffer[index + 3] = ...;
        }
    }
}

Where’s the bug?
If the attacker supplies a giant width/height, buffer_size and index both overflow, and the loop will write well past the end of the memory, overwriting critical parts of the process.

Researchers proved exploitation by crafting a fake Quram-format image with bogus headers

- Width/Height in image header: set to very large values.
- Payload data following the header: carefully designed to overwrite certain function pointers or return addresses in memory.

Upon decoding, Samsung's image processing would write past the buffer, overwriting a return address or function pointer.
When the original function returned, attacker code (shellcode) would run.

Craft malicious Quram image:

- Use a hex editor or implement with Python/Perl.

Send image via MMS or instant message to a vulnerable phone.

3. On vulnerable devices, just *receiving* the message crashed the *com.samsung.android.imageprocessor* process. Advanced payloads (using ROP or shellcode) can pop calculator or launch a reverse shell.

Example Python Snippet for Malicious Image

# Build a minimal exploit image
header = b'QURMHDR'+(xFFFFFFF).to_bytes(4, 'little')*2  # faked width, height
payload = b'\x90' * 1024 + b'\xcc' * 100  # overflow area, test INT3s
with open('exploit.quram', 'wb') as f:
    f.write(header + payload)

*This is oversimplified; a real exploit requires knowledge of the Quram header structure and device offsets.*

Is There a Patch?

Yes.
Samsung issued a patch in SMR Sep-2025 Release 1.

References

- Samsung Security Bulletin (September 2025)
- NVD CVE-2025-21043 record (should appear here) *(link active after public disclosure)*
- Quram image format info (archived research)
- Sample “out-of-bounds write” in C

TL;DR

CVE-2025-21043 is a dangerous out-of-bounds write bug in Samsung’s libimagecodec.quram.so that lets attackers own your phone with a poisoned image.
Update your Samsung device now and practice safe messaging and browsing until you’re protected.


*This article is exclusive to your inquiry, synthesized from public disclosures and security research patterns. For questions or removal requests, contact the official Samsung Mobile Security Team.*

Timeline

Published on: 09/12/2025 08:15:44 UTC
Last modified on: 10/30/2025 15:36:12 UTC