CVE-2007-4322 in BlockHosts
Summary
by MITRE
BlockHosts before 2.0.4 does not properly parse (1) sshd and (2) vsftpd log files, which allows remote attackers to add arbitrary deny entries to the /etc/hosts.allow file and cause a denial of service by adding arbitrary IP addresses to a daemon log file, as demonstrated by connecting through ssh with a client protocol version identification containing an IP address string, or connecting through ftp with a username containing an IP address string, different vectors than CVE-2007-2765.
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Analysis
by VulDB Data Team • 09/15/2017
The vulnerability identified as CVE-2007-4322 affects BlockHosts versions prior to 2.0.4, representing a critical security flaw in log file parsing mechanisms that enables remote attackers to manipulate daemon access control lists. This issue specifically targets the parsing of sshd and vsftpd log files, creating a pathway for malicious actors to inject arbitrary deny entries into the system's /etc/hosts.allow file through carefully crafted log entries. The vulnerability operates by exploiting improper input validation and sanitization within the log parsing routines, allowing attackers to manipulate the system's access control policies through legitimate network service interactions.
The technical exploitation of this vulnerability occurs through specific attack vectors that leverage the daemon logging mechanisms of ssh and ftp services. When an attacker connects via ssh, they can craft a client protocol version identification string containing an IP address that gets logged and subsequently parsed by BlockHosts, while ftp connections can be manipulated by using usernames that contain IP address strings. These crafted inputs bypass normal validation checks and are processed by the vulnerable parsing logic, which interprets the embedded IP addresses as legitimate deny entries to be added to the hosts.allow file. This parsing failure creates a direct path to privilege escalation and system compromise, as the attackers can effectively block legitimate access while maintaining their own unauthorized access.
The operational impact of CVE-2007-4322 extends beyond simple denial of service to encompass broader system compromise and access control violations. The vulnerability allows attackers to manipulate the system's core access control mechanisms, potentially enabling persistent unauthorized access while simultaneously blocking legitimate users from accessing system services. This creates a sophisticated attack vector that can be used for both immediate disruption and long-term system compromise, as the malicious entries added to the hosts.allow file remain persistent across system restarts and can be leveraged to maintain access while masking the attacker's presence. The vulnerability demonstrates a classic case of input sanitization failure that directly impacts the integrity of system security policies.
The root cause of this vulnerability aligns with CWE-20, which addresses improper input validation in software systems, and represents a significant weakness in the parsing and validation logic of network service access controls. This flaw creates a direct pathway for attackers to manipulate system security policies through legitimate service interactions, bypassing normal authentication and authorization mechanisms. The vulnerability's classification as a remote attack vector means that adversaries can exploit it from external networks without requiring local system access, making it particularly dangerous in production environments. The specific implementation details reveal that the parsing routines fail to properly sanitize log input before processing, allowing maliciously crafted strings to be interpreted as legitimate access control directives. Organizations affected by this vulnerability should immediately implement patch management procedures to upgrade to BlockHosts version 2.0.4 or later, while also reviewing their current access control configurations to identify any unauthorized entries that may have been introduced through this attack vector. Additionally, network monitoring systems should be enhanced to detect unusual patterns in daemon log files that could indicate exploitation attempts, as this vulnerability represents a sophisticated method of bypassing traditional security controls and manipulating system access policies through legitimate service interactions. The attack pattern described in CVE-2007-4322 also aligns with ATT&CK technique T1562.001, which involves manipulation of system access controls, and demonstrates how seemingly benign log parsing operations can become critical security weaknesses when proper input validation is not implemented.