What looks like an innocent compressed file can be a hidden cyber weapon. Welcome to the world of zip bombs—cleverly crafted “compressed grenades” that aim to overwhelm systems rather than infect them with malware. These files, though deceptively tiny, can disrupt servers and leave networks vulnerable to further attacks. They have also been used in the past to crash antivirus programs.
This article dives into the anatomy of a zip bomb, the threats they pose to systems, and the weapons security professionals can deploy to combat them and stay ahead of these sly denial-of-service tactics.
A zip bomb, also known as a “decompression bomb” or “zip of death,” is a type of malicious archive file designed to overwhelm a system’s resources when decompressed. Unlike most malware, which corrupts or steals data, zip bombs create chaos by exhausting a system’s CPU, RAM, and storage capacity.
These files often appear harmless and are no larger than a few kilobytes. However, once extracted, their content can explode into terabytes or even petabytes of junk data, crashing any system that attempts to unpack them.
Zip bombs serve two main purposes in cyberattacks:
Disruption: Crash systems or antivirus tools to enable attacker entry.
Diversion: Stall cybersecurity defenses while sneaking in secondary payloads.
Though less common than phishing or ransomware, zip bombs present unique challenges. Their deceptive simplicity makes them a low-cost, high-impact tool for attackers. Here’s why they remain a significant cybersecurity risk:
Many zip bombs are not effectively detected by older antivirus scanners. Some older antivirus programs will try to inspect all the file’s contents, which could take days and leave the system exposed.
Zip bombs can knock servers offline or freeze systems during decompression, effectively creating a DoS attack. This disruption can lock users out of critical operations or leave entire networks vulnerable.
Disguised as ordinary emails or innocuous file uploads, zip bombs often slip through standard filters and deceive users into manual interaction, especially in environments without advanced security tools.
While zip bombs don’t delete or corrupt data, their ability to incapacitate systems is often more devastating than outright destruction.
Zip bombs take advantage of compression algorithms that can shrink massive amounts of data into tiny packages. The simplicity of their function is what makes them so dangerous.
Many zip bombs use multiple layers of nested compression. A single archive file may contain hundreds of compressed folders within, leading to exponential data inflation once fully extracted.
Example: Take the infamous "42.zip," a zip bomb that’s only 42 KB in size but decompresses into 4.5 petabytes of data, thanks to recursive layers of 16 zip files per folder.
More advanced zip bombs use non-recursive methods, where data segments overlap and compress more efficiently. This results in extreme data inflation with fewer layers, making detection harder.
These bombs embed structures that trap decompression algorithms in endless cycles, consuming all available memory and processing power
These contain deeply nested zip files, forcing systems to unpack layer after layer until they collapse under the weight of the inflated data.
Rely on ingenious compression techniques to reduce large datasets into deceptively small files with minimal layering.
Some zip bombs aren’t just about resource exhaustion. They serve as payload carriers, delivering malware after the decompression chaos has crippled defenses.
Staying ahead of zip bomb threats involves combining tools, tactics, and training. Here’s how you can prevent these attacks effectively:
The Huntress SOC ensures false positives are minimized while validating true risks. This targeted approach allows analysts to stay focused on strategic tasks.
Modern decompression tools (e.g., WinRAR, 7-Zip) allow admins to set limits:
Restrict recursion depth to avoid infinite unpacking cycles.
Cap CPU and memory consumption during decompression efforts.
Set extraction size limits for unknown files.
Human error often enables zip bomb success. Leverage security awareness training so your employees know to:
Avoid opening zip files from unknown or unverified sources.
Double-check email links or file origins when in doubt.
Recognize unusual file patterns, such as tiny file sizes claiming to contain significant data.
Participate in information-sharing groups, such as ISACs, to stay informed on emerging zip bomb tactics. Collaborating with an industry-wide defense community increases overall preparedness.
Zip bombs are digital chaos packed in a deceptively tiny file. With tools like endpoint detection and response, and security awareness training, you can safeguard your systems from falling victim to these crafty attacks.
