CVE-2023-30775 - Understanding the libtiff Heap Buffer Overflow Vulnerability and How It’s Exploited

In 2023, security researchers discovered a serious vulnerability labeled CVE-2023-30775 in the widely-used libtiff library. This security flaw occurs due to a heap buffer overflow in the extractContigSamples32bits function, found in the tiffcrop.c file. This post explains what this means, who is affected, and, with a simple code snippet, shows how attackers could exploit it. We’ll also link to original references and recommend mitigation steps.

What is libTIFF and Why Does it Matter?

libTIFF is a free, open-source C library that handles TIFF (Tagged Image File Format) images. Many applications and systems rely on it for manipulating images, including graphics editors, scanners, and even some operating systems.

A vulnerability in libTIFF can ripple out to any software that uses it, making this a critical issue.

Vulnerability Details: What is CVE-2023-30775?

* Type: Heap Buffer Overflow  
* Component: libtiff  
* File: tiffcrop.c  
* Function: extractContigSamples32bits  
* CVSS Score: Check NVD Listing (often HIGH)

The Problem

The vulnerable function, extractContigSamples32bits, is supposed to safely extract pixel data from TIFF images. However, due to a missing check, it will *write* more data to memory than the buffer is allocated for. This enables a classic heap buffer overflow attack.

If an attacker tricks your program into opening a specially-crafted TIFF file, they can corrupt your program’s memory. In practice, this could allow:

Vulnerable Code Snippet

Here’s a simplified (and commented) version of the critical section from the original vulnerability (see upstream diff):

// tiffcrop.c (before fix)
void extractContigSamples32bits(uint32 *image, uint32 *obuf, uint32 cols, 
                                uint32 rows, uint16 samplesperpixel, 
                                uint16 sample)
{
    for (row = ; row < rows; row++) {
        for (col = ; col < cols; col++) {
            *obuf++ = image[(row * cols + col) * samplesperpixel + sample];
        }
    }
}

The issue comes down to not checking if obuf has enough space for the operation. If you supply an image with a large samplesperpixel or crafted rows/cols values, the code will happily overwrite memory (heap) outside of obuf.

Exploit Details: How Could This Be Used?

To *exploit* this bug, an attacker would create a malicious TIFF file. Opening the file in any application that uses a vulnerable version of libtiff will trigger the flaw. Here’s what could happen:

1. Trigger the bug: The TIFF file includes large or negative values for certain fields so the calculations for obuf size are wrong.
2. Heap overflow: As extractContigSamples32bits loops, it goes beyond the end of obuf, corrupting adjacent memory.
3. Control execution: With careful tailoring, the attacker could overwrite security-critical data (like function pointers), gaining control of the process.

Here’s a high-level PoC in C that simulates the overflow caused by opening a malicious file

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

void extractContigSamples32bits(uint32_t *image, uint32_t *obuf, 
                                uint32_t cols, uint32_t rows, 
                                uint16_t samplesperpixel, uint16_t sample)
{
    for (uint32_t row = ; row < rows; row++) {
        for (uint32_t col = ; col < cols; col++) {
            // OVERFLOW: no bounds check on obuf!
            *obuf++ = image[(row * cols + col) * samplesperpixel + sample];
        }
    }
}

int main() {
    // attacker controls these parameters!
    uint32_t cols = 10000, rows = 10000; // very large
    uint16_t samplesperpixel = 4, sample = ;
    uint32_t *image = malloc(cols * rows * samplesperpixel * sizeof(uint32_t));
    uint32_t *obuf = malloc(cols * rows * sizeof(uint32_t)); // too small!

    // simulate processing a malicious TIFF
    extractContigSamples32bits(image, obuf, cols, rows, samplesperpixel, sample);

    free(image); free(obuf);
    printf("Done\n");
}

Warning: The above is for demonstration only. Running code with huge allocations *will* crash or corrupt.

Original commit fixing the bug:

gitlab.com/libtiff/libtiff/-/commit/255a19d7b1c1b63adebc3daa55a7e8e2ec10d77

CVE database entries:

CVE-2023-30775 (MITRE)  
 NVD Entry

Upstream libtiff discussion:

Email thread on the bug

Conclusion

CVE-2023-30775 is a dangerous heap buffer overflow flaw in libtiff. If exploited, it could let attackers crash your app or even take control of it by just tricking you into opening a malicious TIFF file. Patching is critical and easy: upgrade libtiff everywhere you use it.

Feel free to share this post with your colleagues and check your systems’ libtiff version today.


*This post was written to explain the mechanics and risks of CVE-2023-30775 in simple terms, drawing directly from the technical references and demonstrating with sample code.*

Timeline

Published on: 05/19/2023 15:15:00 UTC
Last modified on: 05/26/2023 15:26:00 UTC