CVE-2008-1434 in Office
Summary
by MITRE
Use-after-free vulnerability in Microsoft Word in Office 2000 and XP SP3, 2003 SP2 and SP3, and 2007 Office System SP1 and earlier allows remote attackers to execute arbitrary code via an HTML document with a large number of Cascading Style Sheets (CSS) selectors, related to a "memory handling error" that triggers memory corruption.
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Analysis
by VulDB Data Team • 08/10/2019
This vulnerability represents a critical use-after-free flaw in Microsoft Word's handling of HTML documents containing excessive CSS selectors. The issue manifests when Word processes malformed HTML content with an unusually high number of CSS style rules, leading to improper memory management during document parsing. The root cause lies in the application's failure to properly validate and manage memory allocation when encountering complex CSS structures, creating a scenario where freed memory blocks are accessed after being reallocated, resulting in memory corruption that can be exploited by malicious actors.
The technical exploitation of this vulnerability leverages the memory handling error to overwrite critical memory locations with attacker-controlled data. When Word parses HTML documents with excessive CSS selectors, the application's memory management routines fail to properly track allocated memory blocks, allowing an attacker to craft a malicious document that triggers a use-after-free condition. This condition enables arbitrary code execution with the privileges of the user running Word, potentially allowing full system compromise. The vulnerability specifically affects Microsoft Office versions including Office 2000, XP SP3, 2003 SP2 and SP3, and 2007 Office System SP1 and earlier, making it particularly dangerous due to the widespread deployment of these older Office versions.
The operational impact of this vulnerability extends beyond simple code execution to encompass complete system compromise and potential data exfiltration. Attackers can leverage this flaw to execute malicious payloads without user interaction, as the exploitation occurs during document opening or rendering. The vulnerability's remote exploitation capability means that attackers can deliver malicious HTML documents through email attachments, web downloads, or compromised websites, making it a significant threat vector for enterprise environments where legacy Office installations remain in use. This type of vulnerability directly relates to CWE-416, which describes the use of freed memory condition, and maps to attack techniques in the ATT&CK framework under T1059 for command and scripting interpreter and T1203 for exploitation for client execution.
Mitigation strategies should focus on immediate patching of affected Office versions, as Microsoft released security updates addressing this specific memory handling error. Organizations must also implement strict document filtering policies that restrict the execution of HTML content from untrusted sources, particularly in enterprise environments where legacy systems may not be immediately upgraded. Network-based protections should include web application firewalls and email filtering solutions that can identify and block malicious HTML documents containing excessive CSS selectors. Additionally, user education regarding the dangers of opening suspicious email attachments and visiting untrusted websites remains crucial, as social engineering remains a primary delivery mechanism for such exploits. The vulnerability demonstrates the importance of proper memory management in office applications and highlights why regular security updates and patch management processes are essential for maintaining enterprise security postures.