CVE-2023-32029

What it actually does

This is a remote code execution class vulnerability in which a specially crafted Excel document can cause code to execute when opened by a user. The CVSS vector indicates exploitation requires local user interaction, no prior attacker privileges, and can result in high confidentiality, integrity, and availability impact in the context of the affected user. Successful exploitation can allow an attacker to run arbitrary commands, drop payloads, access files available to the user, and use the compromised endpoint as a foothold for lateral movement. The provided affected-product metadata references cecilapp/cecil with a fixed Git commit, which should be validated against authoritative vendor advisories because it does not align with the Microsoft Excel description.

Why it matters to the business

If exploited, this flaw can turn a malicious spreadsheet into an initial access mechanism for endpoint compromise, data theft, credential harvesting, ransomware staging, or business email compromise. The issue is not listed in CISA KEV and no ransomware usage is indicated in the supplied data, but the EPSS score is elevated, suggesting meaningful exploitation likelihood. Because the vulnerability has been public for more than three years, organizations should assume adversaries have had ample time to incorporate similar document-based lures into phishing tradecraft. Operational impact is highest where users frequently receive external spreadsheets or where macro/file-origin controls are weak.

How an attack unfolds

An attacker typically prepares a malicious Excel file that triggers the vulnerable code path when opened. The attacker delivers the file through phishing email, file-sharing links, compromised collaboration platforms, or other social-engineering channels. A targeted user opens the document on a vulnerable system, causing attacker-controlled code or follow-on commands to execute under that user's permissions. The attacker may then establish persistence, collect documents and credentials, communicate with command-and-control infrastructure, or deploy additional tooling. Because user interaction is required, exploitation commonly depends on convincing delivery themes such as invoices, reports, purchase orders, or business forms.

How to fix it

Apply the relevant Microsoft Office/Excel security updates from the vendor for this vulnerability across all supported Windows and Office channels. If the supplied package metadata is applicable in your software inventory, update cecilapp/cecil to a version containing Git commit 00dc79f10ce723034b7140d79f4ac731d1d902eb and verify the advisory mapping before treating that as the sole fix. Where immediate patching is not possible, reduce exposure by blocking or sandboxing external Office attachments, enforcing Protected View and Mark-of-the-Web controls, disabling unnecessary active content, limiting Office child-process creation through attack surface reduction rules, and ensuring endpoint detection coverage for Office application behavior. Remove unsupported Office versions because they may not receive reliable fixes.

How to confirm the fix worked

Confirm installed Office/Excel versions and patch levels against the vendor's security update guide or enterprise patch-management baseline. Test representative endpoints by verifying that external spreadsheets open in Protected View and that Office child-process prevention controls are active where configured. For the cecilapp/cecil metadata, verify that deployed source or package artifacts include commit 00dc79f10ce723034b7140d79f4ac731d1d902eb or a later trusted revision. Use vulnerability scanners, software inventory, and configuration management to confirm no vulnerable versions remain. Validate compensating controls by reviewing email gateway attachment handling, sandbox detonation results, endpoint policy enforcement, and EDR alerts for Office spawning scripting or shell utilities.

Typical attack path

1. Identify an organization or user likely to open spreadsheet attachments or shared files.
2. Craft or obtain a malicious Excel document designed to trigger the vulnerable code path.
3. Deliver the file through phishing email, cloud file sharing, messaging, or a compromised trusted sender.
4. Wait for a user to open the file on a vulnerable endpoint.
5. Execute code in the context of the logged-in user.
6. Spawn child processes or drop payloads to establish command execution, persistence, or remote access.
7. Harvest credentials, access local/network files, move laterally, or stage data theft/ransomware activity.

How to detect it

Investigate endpoint, email, proxy, DNS, and identity logs for evidence of malicious spreadsheet delivery followed by suspicious execution. Key log sources include EDR process telemetry, Windows Security Event ID 4688 process creation logs, Sysmon Event ID 1 process creation, Sysmon Event ID 11 file creation, PowerShell logs Event IDs 4103 and 4104, Office telemetry, email gateway attachment logs, web proxy downloads, DNS queries, and authentication logs. Look for EXCEL.EXE opening externally sourced files and then spawning child processes such as cmd.exe, powershell.exe, wscript.exe, cscript.exe, mshta.exe, rundll32.exe, regsvr32.exe, certutil.exe, bitsadmin.exe, curl.exe, or wget.exe. Also look for new executables or scripts written to user-writable paths shortly after Excel activity, unusual outbound connections from Office child processes, credential-access tooling, persistence changes, and anomalous sign-ins following document execution. Because no exploit-specific public IOC is provided in the input, detection should focus on behavioral indicators rather than a single hash, filename, or network address.

• EXCEL.EXE cmd.exe
• EXCEL.EXE powershell.exe
• EXCEL.EXE pwsh.exe
• EXCEL.EXE wscript.exe
• EXCEL.EXE cscript.exe
• EXCEL.EXE mshta.exe
• EXCEL.EXE rundll32.exe
• EXCEL.EXE regsvr32.exe
• EXCEL.EXE certutil.exe
• EXCEL.EXE bitsadmin.exe
• EXCEL.EXE curl.exe
• EXCEL.EXE wget.exe
• ParentImage=*\\EXCEL.EXE Image=*\\cmd.exe
• ParentImage=*\\EXCEL.EXE Image=*\\powershell.exe
• ParentImage=*\\EXCEL.EXE Image=*\\wscript.exe
• ParentImage=*\\EXCEL.EXE Image=*\\mshta.exe
• ParentImage=*\\EXCEL.EXE Image=*\\rundll32.exe
• ParentImage=*\\EXCEL.EXE Image=*\\regsvr32.exe
• EventCode=4688 New Process Name=*\\powershell.exe Creator Process Name=*\\EXCEL.EXE
• EventCode=4688 New Process Name=*\\cmd.exe Creator Process Name=*\\EXCEL.EXE
• EventCode=1 ParentImage=*\\EXCEL.EXE Image=*\\powershell.exe
• EventCode=1 ParentImage=*\\EXCEL.EXE Image=*\\cmd.exe
• C:\\Users\\*\\AppData\\Local\\Temp\\*.xls
• C:\\Users\\*\\AppData\\Local\\Temp\\*.xlsx
• C:\\Users\\*\\AppData\\Local\\Temp\\*.xlsm
• C:\\Users\\*\\AppData\\Local\\Temp\\*.xll
• C:\\Users\\*\\AppData\\Roaming\\Microsoft\\Excel\\XLSTART\\*.xll
• C:\\Users\\*\\AppData\\Roaming\\Microsoft\\Excel\\XLSTART\\*.xlsm
• Zone.Identifier
• 00dc79f10ce723034b7140d79f4ac731d1d902eb

What your security team should do

• Prioritize patching vulnerable Office/Excel installations, especially on endpoints used by finance, operations, HR, procurement, executives, and other users who commonly receive spreadsheets.
• Validate the product mapping discrepancy between the Microsoft Excel description and the supplied cecilapp/cecil affected-product metadata before closing remediation tickets.
• Hunt for Office process trees where EXCEL.EXE launches command interpreters, script engines, LOLBins, archive tools, or network utilities.
• Enforce attack surface reduction rules or equivalent EDR controls to block Office applications from creating child processes and executable content.
• Tighten email and collaboration-platform controls for spreadsheet attachments from external or newly observed senders.
• Review endpoint detections for suspicious activity following spreadsheet opens, including payload writes to user-writable directories and outbound connections to rare domains or IPs.
• Educate users to report unexpected spreadsheets, especially invoices, purchase orders, shipping documents, or password-protected archives containing Office files.