CVE-2026-50517: Microsoft M365 Copilot Remote Code Execution Vulnerability

criticalCVSS 9.9CVE-2026-50517

Deserialization of untrusted data in M365 Copilot allows an authorized attacker to execute code over a network.

CSIRTS triage

vendor: Microsoft product: M365 Copilot Remote code execution Unsafe deserialization

What: Deserialization of untrusted data allows an authorized attacker to execute code over a network.
Who is affected: Deployments of M365 Copilot are affected.
Urgency: Remediation is critical due to the high severity and potential for exploitation.
Action: Apply the latest security updates for M365 Copilot.

AI-assisted analysis generated from the source advisory — verify against the original.

⚡ Watch M365 Copilot

Get an email when a new M365 Copilot advisory drops — max one per day, one-click unsubscribe.

Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: critical — CVSS 9.9
Published: 2026-07-14
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-50517

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Moderate exploitation riskCVE-2026-505171.3% 30-day exploitation probability. Patch within normal cadence, watch for KEV listing. Riskier than 67% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-50517	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

Recent advisories for Microsoft M365 Copilot

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highCVE-2026-45497: Microsoft M365 Copilot Remote Code Execution Vulnerabilitymsrc · 2026-06-09