CVE-2015-1770

What Is Microsoft Office?

Microsoft Office is the world's dominant productivity suite, with Word, Excel, PowerPoint, and related applications handling billions of documents daily across enterprise, government, and consumer environments. The complexity of Office's document parsing subsystems — handling dozens of file formats, embedded objects, fonts, macros, and media — creates a large attack surface. Memory corruption vulnerabilities in Office parsers are consistently exploited in targeted spear-phishing attacks because users routinely open documents received by email.

Overview

CVE-2015-1770 is an uninitialized memory use vulnerability (CWE-824) in Microsoft Office that allows a remote attacker to execute arbitrary code by convincing a user to open a specially crafted Office document. The vulnerability occurs when Office accesses a pointer or data value that has not been properly initialized — reading from an unpredictable or attacker-influenced memory location in a way that can redirect code execution. Patched in MS15-059 (June 9, 2015).

Affected Versions

Fixed with MS15-059 (June 2015 Patch Tuesday).

Technical Details

Root Cause: Uninitialized Pointer Access

CVE-2015-1770 involves a code path in Microsoft Office's document processing logic where a pointer or buffer is used before it has been properly initialized. When Office processes a specially crafted document, a conditional path leaves a memory region uninitialized — the code then dereferences that uninitialized pointer, reading from an arbitrary memory location.

If an attacker can influence the uninitialized value (through heap manipulation or careful document construction), the dereference reads attacker-controlled data as a function pointer or vtable entry — redirecting code execution to attacker-chosen code.

Uninitialized memory vulnerabilities are particularly insidious because the behavior is implementation-dependent: in debug builds, memory is often zeroed (making the bug invisible during testing), while in release builds, the heap often contains residual data from previous allocations that can be shaped by the attacker.

Attack Delivery

Standard Office exploit delivery:

1. Attacker sends a malicious Office document via email or web download
2. Recipient opens the document in Microsoft Word, Excel, or PowerPoint
3. The document's crafted structure triggers the uninitialized pointer access
4. Code execution achieved at the user's privilege level

Attack Characteristics

Discovery

Reported to Microsoft and patched in MS15-059 (June 2015 Patch Tuesday), which addressed multiple memory corruption vulnerabilities in Microsoft Office.

Exploitation Context

• Spear-phishing delivery: Microsoft Office RCE vulnerabilities are the backbone of APT spear-phishing campaigns; CVE-2015-1770 was exploited in targeted attacks against organizations with outdated Office versions
• Long exploitation tail: APT groups reuse reliable Office exploits for years after patches are available against organizations with poor patch management; CISA KEV addition in March 2022 confirms exploitation 7 years after the patch
• CISA KEV (2022): Added March 2022

Remediation

1. Apply MS15-059 (June 2015). Any Office installation updated after June 2015 includes this fix.

2. Enable Office Protected View — opens documents from external sources in a sandboxed read-only mode that prevents exploitation of parser vulnerabilities.

3. Maintain current Office updates — Microsoft releases monthly security updates for all supported Office versions.

4. Deploy Attack Surface Reduction (ASR) rules in Microsoft Defender to block Office from creating child processes, reducing post-exploitation impact.