Microsoft Office Use-After-Free Vulnerability

What it is

Microsoft Office contains a use-after-free vulnerability which can allow for remote code execution.

VulnCheck tracked exploitation 1759 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 updates per vendor instructions.

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.

Microsoft fix

• KB3118310 (Security Update)
• KB3172458 (Security Update)
• KB3114375 (Security Update)

Sourced from Microsoft Security Update Guide (CVRF document 2017-May).

CISA due date

Federal deadline: March 24, 2022. 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: 78.1% — higher than 100% 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-2007-0671: Microsoft Office Excel Remote Code Execution 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

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.