CVE-2007-0671

What is Microsoft Office Excel?

Microsoft Excel is the world's most widely used spreadsheet application, part of the Microsoft Office suite. The Excel binary format (.XLS) and its successors have been the standard for financial data, analytics, and business reporting for decades. Excel's complex file format — supporting formulas, macros, charts, embedded objects, and external data connections — has historically contained numerous memory corruption vulnerabilities that could be triggered by opening maliciously crafted .XLS files. Excel is a perennial target for attackers because the combination of ubiquity (nearly every business user has Excel) and rich format complexity creates a large and persistent attack surface.

Overview

CVE-2007-0671 is a high-severity remote code execution vulnerability (CVSS 8.8) in Microsoft Office Excel. Opening a specially crafted Excel file triggers a memory corruption condition that allows arbitrary code execution in the security context of the user running Excel. The vulnerability was patched in Microsoft Security Bulletin MS07-015 (February 2007 Patch Tuesday). Unusually, CISA added this to KEV in August 2025 — 18 years after the original patch — indicating active exploitation of unpatched legacy Office installations in current attack campaigns.

Affected Versions

Technical Details

The vulnerability exists in how Microsoft Excel's binary .XLS file parser handles certain record types or object structures within a crafted spreadsheet file. Excel's .XLS format is a complex binary format (BIFF — Binary Interchange File Format) containing hundreds of record types. The vulnerable code path processes certain record data or object metadata without adequate bounds checking (CWE-120), allowing a crafted file to overwrite adjacent memory.

Exploitation typically follows the pattern used for document format vulnerabilities of this era:

1. The attacker crafts a malicious .XLS file with a carefully structured record that overflows a buffer or corrupts a function pointer
2. The victim receives the file via email attachment or download, and opens it in Excel 2000/2002/2003
3. The memory corruption redirects execution to shellcode embedded in the file or heap-sprayed into memory
4. Code executes with the privileges of the user running Excel — typically a standard user on a workstation, but administrator if running as admin

The "Network" attack vector reflects practical delivery: malicious .XLS files distributed as email attachments, even though the exploit triggers locally.

Discovery

Reported to Microsoft and disclosed alongside the February 2007 Patch Tuesday release as part of MS07-015, which addressed multiple vulnerabilities in Microsoft Office products. The bulletin covered vulnerabilities in Word, Excel, and other Office components.

Exploitation Context

The August 2025 KEV addition for an 18-year-old vulnerability highlights the persistence of legacy software in enterprise environments:

• Legacy Office installations: Organizations in certain industries (manufacturing, utilities, healthcare) often run decades-old Office versions on air-gapped or semi-isolated workstations, particularly where Excel spreadsheets are embedded in operational workflows and upgrading would require significant validation effort
• Unsupported Office versions: Microsoft ended extended support for Office 2003 in April 2014, Office 2007 in October 2017. Systems still running these versions receive no security updates.
• Financial and industrial environments: Attackers targeting operational technology (OT) environments frequently encounter legacy Windows and Office versions; exploiting this vulnerability provides code execution on workstations that may have access to industrial control systems
• Spear phishing persistence: Targeted attacks using custom Excel files crafted to exploit known vulnerabilities in known target software versions can be highly effective against specific high-value targets

Remediation

1. Apply MS07-015 immediately: Any remaining Office 2000/2002/2003/2004 installations should have this patch applied.
2. Upgrade to a supported Office version: Office 2003 and earlier are end-of-life with no security support. Upgrade to Microsoft 365 or a supported perpetual Office version (2019/2021).
3. Enable Protected View: Modern Office versions open downloaded files in Protected View, blocking exploit execution. Ensure this is enabled for internet-sourced and email-sourced files.
4. Block legacy .XLS format at email gateway: If the business does not require legacy binary .XLS files, block them at the email gateway and require .XLSX (Open XML format) which has a smaller parser attack surface.
5. Inventory legacy Office deployments: Conduct an inventory to identify systems still running Office 2003 or earlier, and prioritize upgrade or decommission.