CVE-2023-41175 - Exploiting Integer Overflows in libtiff’s raw2tiff.c for Remote Code Execution

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Overview

On August 29, 2023, a security flaw was disclosed in libtiff, a widely used open-source library for reading and writing TIFF (Tagged Image File Format) images. The vulnerability, tracked as CVE-2023-41175, is found in the file raw2tiff.c. It allows attackers to create malicious TIFF files that exploit multiple integer overflow weaknesses. These overflows can result in heap-based buffer overflows, giving attackers the power to crash applications (Denial-of-Service), and in some cases, execute arbitrary code on affected systems.

Technical Details: Why Does This Happen?

The problem lies in raw2tiff.c, which is part of the libtiff utilities. When libtiff processes a TIFF image, it reads certain values from the file, like size and dimensions, and uses these values to allocate memory buffers. If the attacker manipulates these numbers to be very large or negative (by clever use of integer overflows), the program might:

Write more data than the buffer can handle.

This is the classic setup for a buffer overflow.

Here’s a simplified version of the risky code

uint32_t linebytes = (imagewidth * bitspersample + 7) / 8;
linebuffer = (unsigned char *) _TIFFmalloc(linebytes);
memcpy(linebuffer, imagebuffer, linebytes); // Potential overflow if linebytes is incorrect!

If imagewidth and bitspersample are attacker-controlled and crafted to overflow, linebytes might wrap around to a small value, causing _TIFFmalloc() to allocate insufficient memory. Then, memcpy() will copy *more* data than it should, smashing nearby memory.

Proof-of-Concept Exploit (PoC)

This bug becomes dangerous if raw2tiff or any app using libtiff processes a malicious TIFF file from an untrusted source. Below is a conceptual PoC. (For detailed real PoCs, see the reference links.)

1. Create a malicious TIFF image with exaggerated dimension fields (imagewidth, bitspersample) using a hex editor or a script.

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If the exploit works, this leads either to a segmentation fault, or in a worst-case, arbitrary code execution, depending on the attacker’s payload in the TIFF file.

Denial of Service (DoS): Program crashes when processing the file.

- Arbitrary Code Execution: Attacker can run code with the privileges of the program processing the TIFF file (e.g., image viewer or a server-side application).

A real-world attacker might use this to infect desktops (via image viewers) or breach servers (via file upload features).

How to Fix

The libtiff developers have issued a patch that introduces better checks to prevent integer overflows and buffer overflows. They ensure that calculations like imagewidth * bitspersample don’t wrap around, and allocations always fit the copy.

Patch Example (Simplified)

if (imagewidth > UINT32_MAX / bitspersample) {
    TIFFError("raw2tiff", "Integer overflow detected!");
    return;
}
uint32_t linebytes = (imagewidth * bitspersample + 7) / 8;
linebuffer = (unsigned char *) _TIFFmalloc(linebytes);

References and Further Reading

- NIST National Vulnerability Database: CVE-2023-41175
- libtiff Issue Tracker – Security bug report
- libtiff Commit Fixing the Vulnerability
- OSS-Security Mailing List: Announcement

How to Protect Your System

If you use any software that processes TIFF files (online galleries, image converters, desktop photo tools, etc.), make sure to update libtiff to version 4.5.1 or above. Also, avoid opening TIFF files from untrusted sources until you’ve updated.

Conclusion

CVE-2023-41175 in libtiff’s raw2tiff.c highlights the danger of integer overflows in code that handles complex, user-controlled file formats. This bug had the potential for far-reaching impact due to how widely TIFF processing is used in servers and desktops. Always keep your libraries updated and use secure programming practices to prevent overflow issues!

Timeline

Published on: 10/05/2023 19:15:11 UTC
Last modified on: 11/07/2023 04:20:56 UTC