Microsoft Office Excel Remote Code Execution Vulnerability

What it is

Microsoft Office Excel contains a remote code execution vulnerability that can be exploited when a specially crafted Excel file is opened. This malicious file could be delivered as an email attachment or hosted on a malicious website. An attacker could leverage this vulnerability by creating a specially crafted Excel file, which, when opened, allowing an attacker to execute remote code on the affected system.

VulnCheck tracked exploitation 4527 days before CISA's KEV listing. VulnCheck's broader catalog of in-the-wild exploitation evidence picked this up before it landed on CISA's formal list. Per-CVE fact about this entry; not a population claim about lead time in general.

Who's affected

Affects anyone using Microsoft 365 or Office to compose, store, or send email, documents, or spreadsheets. In a small practice, that's typically where client communications, engagement letters, and case notes live — credential compromise here means an attacker reads everything that platform stores.

What to do

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

If you don't have someone in-house to verify the patch deployed across every endpoint — or you're not sure whether you're affected — that's exactly the kind of triage we do. Book a free 20-minute triage call.

CISA due date

Federal deadline: September 2, 2025. Federal agencies must complete the required action by this date. For private SMBs the deadline is advisory — but treat it as a strong recommendation, especially if you handle regulated data (HIPAA, GLBA, ABA model rules).

EPSS

EPSS score: 42.1% — higher than 99% of all scored CVEs.

EPSS estimates the probability of exploitation activity in the next 30 days. Every entry on this site is already confirmed exploited, so read it as relative urgency among the things you still have open, not as permission to wait.

Score dated 2026-08-12, from the FIRST.org Exploit Prediction Scoring System.

Other exploited Microsoft Office entries

More CISA KEV entries for Microsoft Office. Same product line, same actively-exploited status.

• CVE-2009-0238: Microsoft Office Remote Code Execution
• CVE-2026-21514: Microsoft Office Word Reliance on Untrusted Inputs in a Security Decision Vulnerability
• CVE-2026-21509: Microsoft Office Security Feature Bypass Vulnerability
• CVE-2009-0556: Microsoft Office PowerPoint Code Injection Vulnerability
• CVE-2023-23397: Microsoft Office Outlook Privilege Escalation Vulnerability
• CVE-2023-21715: Microsoft Office Publisher Security Feature Bypass Vulnerability
• CVE-2009-0563: Microsoft Office Buffer Overflow Vulnerability
• CVE-2013-1331: Microsoft Office Buffer Overflow Vulnerability

Browse more

• All Microsoft KEV entries
• All SMB-relevant KEV entries

Source

This entry comes from CISA's Known Exploited Vulnerabilities catalog, public US-Government data we pull daily. The plain-language framing and the what-to-do guidance above are ours. View the original entry on cisa.gov.