CVE-2004-1773 in sharutils
Summary
by MITRE
Multiple buffer overflows in sharutils 4.2.1 and earlier may allow attackers to execute arbitrary code via (1) long output from wc to shar, or (2) unknown vectors in unshar.
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Analysis
by VulDB Data Team • 06/30/2021
The vulnerability identified as CVE-2004-1773 represents a critical security flaw in the sharutils package version 4.2.1 and earlier, specifically targeting buffer overflow conditions that can be exploited to execute arbitrary code on affected systems. This vulnerability affects the shar and unshar utilities which are commonly used for packaging and extracting shell archive files, making it particularly dangerous in environments where automated processing of shell archives occurs. The flaw stems from inadequate input validation and buffer size management within the command line processing functions of these utilities, creating opportunities for attackers to craft malicious inputs that exceed allocated memory boundaries.
The technical implementation of this vulnerability manifests through two distinct attack vectors that exploit different components of the sharutils suite. The first vector involves the manipulation of output from the wc command when processed through shar, where attackers can craft unusually long output strings that overflow the intended buffer space allocated for processing. The second vector targets the unshar utility through unspecified means that allow for similar buffer overflow conditions during the unpacking process of shell archives. Both attack paths leverage the fundamental weakness of insufficient boundary checking in string handling operations, where the utilities fail to properly validate input lengths before copying data into fixed-size buffers. This vulnerability directly maps to CWE-121, which describes heap-based buffer overflow conditions, and CWE-122, which addresses stack-based buffer overflow scenarios, depending on the specific execution context and memory allocation patterns during processing.
The operational impact of CVE-2004-1773 extends beyond simple privilege escalation to encompass full system compromise when exploited successfully. Attackers can leverage these buffer overflows to inject and execute malicious code with the privileges of the user running the affected utilities, potentially leading to complete system takeover. The vulnerability is particularly concerning in automated environments where shell archives are processed without proper input sanitization, such as in build systems, automated testing frameworks, or web applications that handle user-uploaded shell archives. Additionally, the attack surface is broadened by the widespread use of sharutils across various unix-like systems, making this vulnerability applicable to numerous platforms and installations. The exploitation techniques align with ATT&CK tactics including privilege escalation and execution through the use of system utilities that are typically trusted and widely available on target systems.
Mitigation strategies for CVE-2004-1773 should prioritize immediate patching of affected systems with updated sharutils versions that contain proper input validation and buffer size management. System administrators should implement strict input validation on all shell archive processing workflows, particularly in automated environments where untrusted inputs may be processed. The use of sandboxed execution environments or privilege separation when handling shell archives can significantly reduce the potential impact of successful exploitation attempts. Additionally, network-level controls such as firewall rules that restrict access to systems processing shell archives, combined with regular security auditing of system utilities, can help prevent exploitation attempts. Organizations should also consider implementing runtime protections such as stack canaries or address space layout randomization to make exploitation more difficult even if patches are not immediately available. The vulnerability demonstrates the critical importance of input validation in system utilities and highlights the need for regular security assessments of commonly used unix tools that may not receive frequent security updates.