CVE-2026-50517: Deserialization of untrusted data in M365 Copilot allows an authorized attacker to execute code over a network

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CRITICAL 9.9WATCHLISTMITIGATE

CVE-2026-50517 is a critical-severity flaw (CVSS 9.9) affecting 365 copilot. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Critical severity
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.9 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.7% (top 23%)
CISA exploited list	No
Weakness	CWE-502
Published	2026-07-24
Last modified	2026-10-24

Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Last updated 2026-10-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-24 01:17 UTCPublished CVE record published
2026-10-24 13:10 UTCUpdated Record last modified

microsoft 365 copilot MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy 365-copilot || rpm -q 365-copilot || 365-copilot --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · gnome-shell-extension-tiling-assistant · FIXED · 56-1.fc46 · FEDORA-2026-ebf66a5321 · source

sudo dnf upgrade --advisory=FEDORA-2026-ebf66a5321

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-50517?

365 copilot: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-50517 being exploited?

CVE-2026-50517 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-50517 affect?

CVE-2026-50517 affects 365 copilot. Severity is critical (CVSS 9.9). Deserialization of untrusted data in M365 Copilot allows an authorized attacker to execute code over a network.

How urgent is CVE-2026-50517?

Priority 59/100. Critical severity; On your watchlist

References

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