CVE-2007-2765 in blockhosts
Summary
by MITRE
blockhosts.py in BlockHosts before 2.0.3 does not properly parse daemon 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 logging in through ssh using a login name containing certain strings with an IP address, which is not properly handled by a regular expression, a related issue to CVE-2006-6301.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 09/02/2018
The vulnerability described in CVE-2007-2765 affects the blockhosts.py script in BlockHosts versions prior to 2.0.3, presenting a significant security flaw that enables remote attackers to manipulate system access controls and potentially cause denial of service conditions. This issue stems from improper parsing of daemon log files, specifically targeting the /etc/hosts.allow file which serves as a critical access control mechanism for Unix-based systems. The vulnerability operates through a sophisticated attack vector that leverages the interaction between log file processing and regular expression handling, creating a pathway for unauthorized system modifications that can severely impact network security posture.
The technical flaw manifests in the script's inadequate handling of regular expressions when processing daemon log entries, particularly those generated during SSH authentication attempts. When users log in through SSH using login names containing specific string patterns followed by IP addresses, the blockhosts.py script fails to properly sanitize or validate these inputs before incorporating them into the hosts.allow file. This improper input validation creates a path for attackers to inject malicious IP addresses into the system's access control configuration, effectively allowing them to bypass normal authentication mechanisms and gain unauthorized access to services protected by tcpd (tcpwrappers). The vulnerability is categorized under CWE-20, which represents improper input validation, and specifically relates to CWE-77, which deals with command injection vulnerabilities that can occur when user-supplied data is improperly handled in security contexts.
The operational impact of this vulnerability extends beyond simple access control bypass to encompass potential denial of service scenarios that can severely compromise system availability and integrity. Attackers can exploit this weakness to flood the hosts.allow file with arbitrary IP addresses, effectively creating a denial of service condition where legitimate users may be denied access to critical services, while simultaneously allowing malicious actors to establish persistent access paths. The vulnerability's relationship to CVE-2006-6301 demonstrates a pattern of similar input handling flaws in security tooling that can be leveraged to undermine fundamental system protections. This type of vulnerability directly impacts the principle of least privilege by allowing unauthorized modifications to system-level access controls, potentially enabling attackers to escalate their privileges or establish backdoors within the network infrastructure.
Mitigation strategies for this vulnerability should focus on implementing proper input validation and sanitization measures within the blockhosts.py script, ensuring that all user-supplied data undergoes rigorous parsing and validation before being incorporated into system configuration files. System administrators should immediately upgrade to BlockHosts version 2.0.3 or later, which contains the necessary fixes for the regular expression handling issues. Additionally, implementing proper logging and monitoring mechanisms can help detect unauthorized modifications to the hosts.allow file, while network segmentation and firewall rules can provide additional layers of defense against exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1078 for valid accounts and T1562 for impeding defenses, highlighting the need for comprehensive security controls that address both the immediate vulnerability and broader attack surface considerations. Organizations should also consider implementing automated patch management processes to ensure timely deployment of security updates and reduce the window of exposure to known vulnerabilities.