CVE-2008-2309 in Mac OS X Server
Summary
by MITRE
Incomplete blacklist vulnerability in CoreTypes in Apple Mac OS X before 10.5.4 allows user-assisted remote attackers to execute arbitrary code via a (1) .xht or (2) .xhtm file, which does not trigger a "potentially unsafe" warning message in (a) the Download Validation feature in Mac OS X 10.4 or (b) the Quarantine feature in Mac OS X 10.5.
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Analysis
by VulDB Data Team • 08/12/2019
The vulnerability described in CVE-2008-2309 represents a critical security flaw in Apple Mac OS X operating systems prior to version 10.5.4, specifically within the CoreTypes framework that handles file type recognition and validation. This issue stems from an incomplete blacklist implementation that fails to properly identify and block potentially dangerous file extensions, creating a significant attack surface for malicious actors. The vulnerability specifically affects two file extensions .xht and .xhtm which are not adequately filtered by the system's security mechanisms, allowing these files to bypass important safety checks that would normally prevent execution of untrusted content.
The technical flaw manifests in the Download Validation feature present in Mac OS X 10.4 and the Quarantine feature in Mac OS X 10.5, both of which rely on comprehensive blacklists to identify potentially unsafe file types. When a user downloads a file with a .xht or .xhtm extension, the system fails to recognize these as potentially dangerous file types that require additional security warnings or restrictions. This incomplete filtering mechanism means that attackers can craft malicious files with these extensions that will be silently accepted by the operating system without triggering the appropriate security prompts that would normally alert users to potential risks. The vulnerability specifically leverages the fact that these file extensions are not included in the system's security validation checks, allowing them to be executed without proper sandboxing or user confirmation.
The operational impact of this vulnerability is severe as it enables user-assisted remote code execution attacks where an attacker can deliver malicious payloads through seemingly legitimate file downloads. Attackers can exploit this by hosting malicious .xht or .xhtm files on web servers or sending them via email attachments, knowing that users will not receive security warnings when downloading these files. The attack requires user interaction to initiate the download process, but once downloaded, the files can execute arbitrary code on the target system without the normal security protections that would be applied to other potentially dangerous file types. This creates a significant risk for users who may unknowingly download and execute malicious content, potentially leading to complete system compromise, data theft, or further network infiltration.
This vulnerability maps to CWE-20, "Improper Input Validation," and aligns with several ATT&CK techniques including T1059.007 for command and scripting interpreter and T1068 for exploit for privilege escalation. The incomplete blacklist represents a fundamental flaw in the security architecture where the system's trust model is compromised by inadequate validation of file types. Organizations should implement immediate mitigations including updating to Mac OS X 10.5.4 or later, which contains the necessary security patches to properly handle these file extensions. Additional protective measures include implementing network-level filtering to block downloads of these specific file types, educating users about the risks of downloading unknown files, and ensuring that security software is properly configured to detect and block potentially malicious content. The vulnerability highlights the importance of comprehensive security testing and validation of security mechanisms to prevent such gaps in protection that could be exploited by attackers.