What is CVE-2026-78501?

CVE-2026-78501 is a high-severity vulnerability in Microsoft 365 Copilot Chat, classified under Command Injection. CVSS score: 8.6/10. Published 2026-09-17.

How severe is CVE-2026-78501?

High severity. CVSS v3 base score is 8.6 out of 10.

RCE in Microsoft 365 Copilot Chat

CVE-2026-78501

Improper neutralization of special elements used in a command ('command injection') in Microsoft 365 Copilot's Business Chat allows an unauthorized attacker to disclose information over a network.

Vulnerability class: Command Injection (OS Command Injection)

Published 2026-09-17 · last modified 2026-10-14.

CVSS v3 metric

CVSS v3 base score 8.6 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.005 (45.4th percentile), scored 2026-11-03.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 45th percentile — 45.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.005 · change: -0.004

Affected products

Weakness classification (CWE)

References

Microsoft 365 Copilot Business Chat Information Disclosure Vulnerability (vendor-advisory, Patch, patch, Vendor Advisory)

Frequently asked questions

What is CVE-2026-78501?: CVE-2026-78501 is a high-severity vulnerability in Microsoft 365 Copilot Chat, classified under Command Injection. CVSS score: 8.6/10. Published 2026-09-17.
How severe is CVE-2026-78501?: High severity. CVSS v3 base score is 8.6 out of 10.