CVE-2006-4338 in gzip
Summary
by MITRE
unlzh.c in the LHZ component in gzip 1.3.5 allows context-dependent attackers to cause a denial of service (infinite loop) via a crafted GZIP archive.
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Analysis
by VulDB Data Team • 06/08/2017
The vulnerability identified as CVE-2006-4338 resides within the LHZ component of gzip version 1.3.5, specifically in the unlzh.c file responsible for handling LZH compression format decompression. This flaw represents a classic case of inadequate input validation where the decompression routine fails to properly handle malformed or crafted archive structures, leading to a predictable system behavior that can be exploited for denial of service attacks. The issue manifests when the decompression algorithm encounters a specially constructed GZIP archive that contains malformed LZW (Lempel-Ziv-Welch) compressed data sequences, causing the decompression process to enter an infinite loop state.
From a technical perspective, the vulnerability stems from the lack of proper bounds checking and state validation within the LZW decompression algorithm implementation. When processing compressed data streams, the unlzh.c module does not adequately verify the integrity of the compression headers or the sequence of literal and dictionary reference codes that form the core of LZW compression. This absence of validation allows attackers to craft archive files where the decompression algorithm's internal state becomes corrupted or enters a loop where it continuously references dictionary entries that do not correspond to valid data, resulting in an infinite loop that consumes system resources indefinitely. The flaw operates within the context of decompression operations and requires specific conditions to be met, making it context-dependent rather than universally exploitable.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it can effectively render systems unusable by consuming CPU cycles and memory resources in an unbounded manner. When an affected system attempts to decompress a crafted archive, the infinite loop causes the process to remain active and unresponsive, potentially leading to system instability or complete service unavailability. This makes the vulnerability particularly dangerous in environments where automated decompression processes are common, such as web servers processing user-uploaded files or systems that automatically extract archives from untrusted sources. The denial of service aspect aligns with attack patterns documented in the ATT&CK framework under the T1499 category for network denial of service, while the implementation flaw corresponds to CWE-129 which addresses insufficient validation of length fields.
Mitigation strategies for this vulnerability primarily involve upgrading to newer versions of gzip where the decompression logic has been properly hardened against malformed inputs. System administrators should prioritize patching affected systems and implementing proper input validation at the application level when processing compressed archives. Additionally, deployment of intrusion detection systems that can identify suspicious archive processing patterns may provide early warning of exploitation attempts. Organizations should also consider implementing sandboxing mechanisms for decompression operations and establishing strict file type validation to prevent automatic processing of untrusted archives. The vulnerability serves as a reminder of the critical importance of proper input validation and bounds checking in compression libraries, as similar issues have been documented in various other compression formats and can lead to significant operational disruptions when exploited in the wild.