CVE-2006-1306 in Excel
Summary
by MITRE
Microsoft Excel 2000 through 2004 allows user-assisted attackers to execute arbitrary code via a .xls file with a crafted BIFF record with an attacker-controlled array index that is used for a function pointer, aka "Malformed OBJECT record Vulnerability."
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Analysis
by VulDB Data Team • 07/12/2021
The vulnerability identified as CVE-2006-1306 represents a critical buffer overflow flaw in Microsoft Excel versions 2000 through 2004 that stems from improper handling of malformed BIFF (Binary Interchange File Format) records within Excel files. This vulnerability specifically manifests when Excel processes a .xls file containing a crafted OBJECT record that manipulates an attacker-controlled array index used for function pointer resolution. The flaw resides in the parsing logic that fails to validate array bounds before using user-supplied indices to access function pointers, creating a classic buffer overflow condition that can be exploited to execute arbitrary code with the privileges of the victim user. This issue falls under CWE-125, which describes out-of-bounds read conditions, and CWE-787, which covers out-of-bounds write vulnerabilities, making it particularly dangerous in the context of office productivity software where users frequently open files from untrusted sources.
The technical exploitation of this vulnerability requires an attacker to craft a malicious .xls file containing a specially constructed BIFF record that triggers the flawed array indexing logic. When a victim opens this crafted file, Excel's parser processes the OBJECT record and uses an attacker-controlled index value to access a function pointer array. If the index exceeds the valid array bounds, the application attempts to execute code from an arbitrary memory location, potentially allowing remote code execution. The vulnerability is classified as user-assisted because it requires the victim to open the malicious file, but the attack can be delivered through various social engineering techniques including email attachments, web downloads, or file sharing platforms. This aligns with ATT&CK technique T1059.005 for command and scripting interpreter, where attackers leverage Office applications to execute malicious code through file-based attacks.
The operational impact of CVE-2006-1306 is significant given the widespread deployment of affected Excel versions in enterprise environments and the ease with which attackers can deliver malicious files. Organizations running Microsoft Excel 2000 through 2004 are at risk of complete system compromise when users open malicious documents, as the vulnerability allows for privilege escalation and persistent access to target systems. The attack vector is particularly concerning because it can be delivered through legitimate file sharing channels and email attachments, making it difficult to detect and prevent through traditional network security measures. The vulnerability affects not only individual users but also enterprise networks where Excel files are commonly shared and opened, potentially creating a propagation vector for malware and other malicious software. Security professionals should note that this vulnerability was particularly dangerous in corporate environments where legacy software versions were still in use, as these systems often lacked proper patch management procedures.
Mitigation strategies for CVE-2006-1306 primarily involve immediate patching of affected Microsoft Excel versions through official Microsoft security updates, as well as implementing administrative controls to restrict the execution of potentially malicious files. Organizations should consider disabling the automatic execution of macros and implementing strict file validation policies for Excel files received from external sources. Network administrators should deploy email filtering solutions that can detect and block malicious Excel files, while endpoint protection solutions should be configured to scan and quarantine suspicious file attachments. The vulnerability also highlights the importance of regular security assessments and patch management procedures, as this flaw existed for several years before Microsoft released a comprehensive fix. Organizations should also consider implementing application whitelisting policies to prevent execution of untrusted Office documents and ensure that legacy software versions are properly deprecated to reduce attack surface exposure.