CVE-2010-0001 in gzip
Summary
by MITRE
Integer underflow in the unlzw function in unlzw.c in gzip before 1.4 on 64-bit platforms, as used in ncompress and probably others, allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via a crafted archive that uses LZW compression, leading to an array index error.
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Analysis
by VulDB Data Team • 04/29/2026
The vulnerability described in CVE-2010-0001 represents a critical integer underflow condition that affects the gzip compression utility and its derivatives on 64-bit systems. This flaw exists within the unlzw function located in the unlzw.c source file, which handles decompression of LZW-compressed data streams. The issue manifests specifically when processing crafted archive files that exploit the mathematical properties of integer arithmetic in the decompression process, creating a scenario where expected positive values become negative due to overflow behavior.
The technical implementation of this vulnerability stems from improper handling of integer values during the LZW decompression algorithm execution. When the decompression routine processes malformed input data, it fails to properly validate the bounds of integer calculations, resulting in an underflow condition that can cause the application to allocate memory at invalid addresses or access arrays using negative indices. This particular flaw is specific to 64-bit platforms where the size differences between data types can amplify the impact of integer arithmetic errors. The vulnerability classifies under CWE-191 Integer Underflow, which is a well-documented weakness in software security that occurs when a calculation results in a value that is outside the range of valid values for the data type being used.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially enable remote code execution in certain circumstances. Attackers can craft malicious compressed archives that, when processed by vulnerable applications, trigger the integer underflow condition. This can result in application crashes that disrupt service availability, or more critically, allow attackers to manipulate memory layout and potentially execute arbitrary code with the privileges of the affected process. The vulnerability affects not only the core gzip utility but also ncompress and other applications that utilize the same decompression code path, creating a widespread impact across multiple software implementations that rely on LZW compression algorithms. This type of vulnerability aligns with ATT&CK technique T1059.007 Command and Scripting Interpreter: Unix Shell, as exploitation often involves crafting input that triggers the vulnerable decompression routines, and T1499.004 Network Denial of Service, since the primary impact includes service disruption.
Mitigation strategies for CVE-2010-0001 require immediate patching of affected systems to upgrade to gzip version 1.4 or later, which contains the necessary fixes for the integer underflow condition. System administrators should also implement input validation controls and restrict processing of untrusted compressed files through sandboxed environments or dedicated decompression services. Additionally, network-level filtering can be employed to prevent transmission of suspicious compressed data, while monitoring systems should be configured to detect unusual patterns of decompression activity that might indicate exploitation attempts. Organizations should also conduct thorough vulnerability assessments to identify all systems that might be using affected versions of ncompress or other derivative applications that share the same vulnerable code path, ensuring comprehensive protection across their infrastructure.