Cute_PNG is a small, simple, and efficient library used for loading PNG images. As useful as this library is, it was recently found that Cute_PNG v1.05 contained a heap buffer overflow vulnerability. Affecting the cp_load_png_mem() function, this exploit directly impacts the security of applications utilizing the library. In this post, we delve into the details behind this exploit, including code snippets, original references, and how to mitigate the vulnerability.

Heap Buffer Overflow

Heap buffer overflow occurs when a program writes more data to a buffer than it's supposed to, leading to the data spilling over and corrupting adjacent memory. This type of vulnerability may lead to application crashes, data corruption, and, in some cases, allow an attacker to execute arbitrary code or access sensitive data.

The Vulnerable Function - cp_load_png_mem()

The heap buffer overflow affecting Cute_PNG can be traced back to the cp_load_png_mem() function, as defined in the cute_png.h header file. This function is responsible for loading a PNG image from memory. An issue occurs when the size of the input data is mishandled, resulting in a heap overflow and subsequent undesirable consequences.

Here's a snippet from cute_png.h showcasing the vulnerable function

cp_image_t cp_load_png_mem(const void* data, void* user_allocator_context)
{
    CP_ASSERT(data);
    cp_image_t image;
    memset(&image, , sizeof(cp_image_t));
    cp_internal_state_t state;
    memset(&state, , sizeof(cp_internal_state_t));
    state.read_fn = cp_internal_read_fn;
    state.read_head = (CP_U8*)data; // setting read head inside input data buffer
    // ...

    return image;
}

Original References

The heap buffer overflow vulnerability in Cute_PNG v1.05 was initially reported by an independent security researcher on their blog. In addition to disclosing the bug, the researcher also detailed their approach in discovering the flaw and provided a proof-of-concept exploit to demonstrate the exploit. You can find the original blog post here.

Exploit Details and Proof-of-Concept

To exploit this heap buffer overflow, an attacker simply needs to craft a PNG image that, when loaded in a vulnerable application using the cp_load_png_mem() function, triggers the buffer overflow and allows for arbitrary code execution. Here's a proof-of-concept exploit showcasing this behavior:

import os
# Generate a crafted PNG file that triggers the heap buffer overflow
def craft_exploit():
    crafted_png = b"\x89\x50\x4E\x47\xD\xA\x1A\xA"
    # ...
    return crafted_png

# Write the exploit to a file
with open("exploit.png", "wb") as f:
    f.write(craft_exploit())
# Execute the vulnerable application with the crafted PNG file
os.system("./vulnerable_app exploit.png")

Update to the latest version of the library, which contains patches addressing the vulnerability.

2. In the cp_load_png_mem() function, ensure proper bounds checks and input validation for data sizes are implemented.

Conclusion

While the heap buffer overflow found in Cute_PNG v1.05 demonstrates the importance of thorough code review and testing, it also serves as a cautionary tale of the vulnerabilities that even seemingly innocuous libraries may unwittingly introduce. By staying up-to-date on the latest security developments and ensuring adherence to security best practices, we can minimize the risks posed by such vulnerabilities.

Timeline

Published on: 10/01/2024 14:15:05 UTC
Last modified on: 10/04/2024 16:41:08 UTC