CVE-2005-0687 in Hashcash
Summary
by MITRE
Format string vulnerability in Hashcash 1.16 allows remote attackers to cause a denial of service (memory consumption) and possibly execute arbitrary code via format string specifiers in a reply address, which is not properly handled when printing the header.
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Analysis
by VulDB Data Team • 06/07/2019
The vulnerability identified as CVE-2005-0687 represents a critical format string flaw in the Hashcash 1.16 implementation that exposes systems to both denial of service and potential arbitrary code execution attacks. This vulnerability specifically affects the handling of reply addresses within the hashcash utility, which is commonly used for anti-spam measures and distributed computing applications. The flaw occurs when the system processes format string specifiers embedded within reply addresses without proper sanitization or validation, creating an exploitable condition that can be leveraged by remote attackers.
The technical root cause of this vulnerability stems from improper input validation and handling within the hashcash utility's message processing functions. When a reply address contains format string specifiers such as %s, %d, or other formatting directives, the application fails to properly escape or sanitize these characters before using them in printf-style functions. This improper handling creates a classic format string vulnerability that allows attackers to manipulate memory contents and potentially execute arbitrary code. The vulnerability is particularly dangerous because it operates at the application level, bypassing many traditional network security controls and operating system protections.
From an operational impact perspective, this vulnerability enables attackers to consume excessive system memory through carefully crafted format string specifiers, leading to denial of service conditions that can render hashcash services unavailable to legitimate users. The memory consumption occurs as the application attempts to interpret and process the malformed format specifiers, potentially causing stack corruption or heap memory exhaustion. In more severe cases where the vulnerability is successfully exploited, attackers can achieve arbitrary code execution, potentially elevating their privileges and gaining full control over the affected system. This makes the vulnerability particularly attractive to threat actors targeting systems that rely on hashcash for spam prevention or distributed computing tasks.
The vulnerability aligns with CWE-134, which specifically addresses format string vulnerabilities in software applications. According to the ATT&CK framework, this represents a technique for privilege escalation and denial of service through application-level exploitation. Organizations utilizing hashcash implementations should immediately implement mitigations including input validation, proper format string handling, and regular security updates. The recommended approach involves sanitizing all user-provided input before processing, implementing proper bounds checking, and avoiding direct use of user-controlled data in printf-style functions. Additionally, system administrators should consider implementing network-level controls and monitoring to detect suspicious format string patterns in incoming traffic, as well as maintaining up-to-date security patches for all hashcash implementations in use.