CVE-2015-1642

What Is Microsoft Office?

Microsoft Office is the dominant productivity suite used across enterprise, government, and consumer environments worldwide. Word, Excel, and PowerPoint collectively handle billions of documents containing complex structured content. The parsers for Office document formats (doc, docx, xls, xlsx, ppt, pptx, rtf, and others) are large, complex codebases with extensive legacy code — historically a significant source of memory corruption vulnerabilities.

Office memory corruption vulnerabilities delivered via malicious documents are among the most effective targeted attack vectors: users routinely open documents received by email, and document files pass through security filters more easily than executable code.

Overview

CVE-2015-1642 is a memory corruption vulnerability in Microsoft Office that allows remote code execution when a user opens a specially crafted Office document. The vulnerability was exploited in targeted attacks against organizations that had not applied the August 2015 Patch Tuesday updates. Patched in MS15-081 (August 11, 2015).

Affected Versions

Systems patched with MS15-081 are not vulnerable.

Technical Details

Root Cause: Memory Corruption in Document Object Handling

CVE-2015-1642 involves out-of-bounds write memory corruption (CWE-787) in Microsoft Office's handling of document content. When processing a maliciously crafted Office document, the application writes data beyond the bounds of an allocated buffer — corrupting adjacent heap memory in a way that can redirect execution to attacker-controlled code.

Office memory corruption vulnerabilities frequently involve complex document structures that trigger edge cases in parsing logic: unexpected property combinations, large arrays with miscalculated sizes, embedded object hierarchies that violate format assumptions, or format-specific structures with inconsistent length fields.

Standard Attack Delivery

1. Email delivery — attacker sends a malicious Office document as an email attachment to targeted users
2. User opens document — in Word, Excel, or PowerPoint
3. Memory corruption triggered — the vulnerable parsing code writes out of bounds
4. Code execution — with heap manipulation, the attacker achieves code execution in the Office application's process context
5. Payload delivered — typically a downloader or backdoor

Attack Characteristics

Discovery

Reported to Microsoft and patched in MS15-081 (August 2015 Patch Tuesday), which addressed multiple memory corruption and privilege escalation vulnerabilities in Microsoft Office.

Exploitation Context

• Targeted APT campaigns: Microsoft Office memory corruption vulnerabilities are a mainstay of APT toolkits; CVE-2015-1642 was exploited in targeted attacks against organizations that had not applied the August 2015 patch
• Spear-phishing delivery: Weaponized Office documents sent to specific individuals — particularly in government, defense, and financial sectors — with lure content tailored to the target's role
• Long exploitation tail: Organizations with poor Office patch management or those running unsupported Office versions remain vulnerable to this class of vulnerability for years after patches are available
• CISA KEV (2022): Added March 2022, confirming continued active exploitation

Remediation

1. Apply MS15-081 (August 2015). Any Office installation updated after August 2015 includes this fix.

2. Maintain current Office updates — Microsoft releases monthly security updates for all supported Office versions; current patch levels eliminate this vulnerability.

3. Enable Office Protected View — sandbox documents from external sources (email, internet downloads) in read-only mode to prevent automatic exploitation.

4. Deploy Attack Surface Reduction (ASR) rules — rules blocking Office from creating child processes significantly reduce post-exploitation impact.

5. Migrate to Microsoft 365 — Microsoft 365 Apps for Enterprise receives security updates automatically and is the recommended path for organizations still running Office 2013 or earlier.