In 2022, a security flaw was discovered in the popular Libtiff library, specifically within the tiffcp command-line tool. The flaw, tracked as CVE-2022-1355, lets attackers trigger a stack buffer overflow bug by simply feeding a specially-crafted TIFF image to tiffcp. This post explains the vulnerability in simple terms, shows a code snippet where the problem lies, and explains how it may be exploited to crash the tool and potentially deny service to users. This post is based on the original advisory and code review.

What is Libtiff and tiffcp?

Libtiff is an open-source library for reading and writing TIFF image files. It's widely used in graphics software, image converters, and even scientific tools.

The tiffcp utility, included with Libtiff, copies and converts TIFF files. It's often used by administrators and image professionals for file manipulation.

Here's a typical usage

tiffcp input.tiff output.tiff

About the Flaw: What is Stack Buffer Overflow?

When a program tries to write data past the edge of a small buffer on the stack, it can overwrite other data in memory. This is called a stack buffer overflow. If an attacker can trigger this, they may crash the program or, in rare cases, run malicious code.

Where is the Problem?

The issue was found in the main() function in tools/tiffcp.c. Here's a simplified version of the problematic code section:

char mode[10];
...
if (compression == COMPRESSION_JPEG) {
    ...
    strcpy(mode, "w"); // mode is a small buffer
    if (quality > 75)
        strcat(mode, "b"); // unguarded append!
    if (compressionOption)
        strcat(mode, compressionOption); // may overflow!
}

If a malicious TIFF file contains a crafted compression option, the compressionOption string could be too long, overrunning the mode buffer allocated on the stack.

Reference

- MITRE CVE-2022-1355
- Libtiff GitLab issue #348

Craft a Malicious TIFF: The attacker creates a TIFF file with an overly long compression option.

2. Invoke tiffcp: The victim or automation (like a web app), thinking the file is safe, runs tiffcp with the file as input.
3. Crash the Program: When tiffcp parses the file, it overflows the mode buffer, corrupting memory and likely causing a crash (segmentation fault).

Simple Proof of Concept

While it can be tricky to build a malicious TIFF from scratch (most users don't do this by accident), one can simulate the vulnerability with command-line tiffcp arguments if a protocol were used that let the attacker control compression options.

Here's a minimal reproducer simulated in code

// Dangerous usage (pseudocode)
char mode[10] = "w";
char user_input[100] = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
// Suppose user_input is from a TIFF file
strcat(mode, user_input); // Will overflow mode buffer!

If you run this with a real tiffcp tool and control the input, it will crash.

Mitigation and Fix

After the issue was reported, Libtiff maintainers fixed the code by replacing unsafe string operations (strcpy, strcat) with bounded alternatives like strncpy, strncat, and by checking buffer lengths before copying.

Action for Users:

Why Does This Matter?

Many open-source tools depend on Libtiff, including servers, image processors, and even scientific software. A denial of service could block those apps from running, or worse—if new techniques are found—something more dangerous could happen.

Summary

CVE-2022-1355 is a stack buffer overflow in Libtiff’s tiffcp tool, caused by unprotected buffer copying. Feeding tiffcp a specially-fashioned TIFF file can crash it, making the software unreliable in automated systems dealing with user uploads or batch image conversions.

Takeaway: Always keep your libraries up to date, and be wary of processing files from untrusted sources!

More Reading:  
- Official Libtiff Downloads
- CWE-121: Stack-based Buffer Overflow


*Author's note: This explanation is written exclusively to break down CVE-2022-1355 in plain language for everyday users and sysadmins, showing the simple but important risks of buffer overflows in command-line tools.*

Timeline

Published on: 08/31/2022 16:15:00 UTC
Last modified on: 11/07/2022 19:12:00 UTC