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CVE-2026-50517 is a critical remote code execution vulnerability in Microsoft M365 Copilot caused by deserialization of untrusted data. The flaw allows an authorized attacker with low privileges to send malicious serialized data to a network-accessible Copilot service endpoint and trigger code execution within the backend service context. The vulnerability is associated with CWE-502 and affects the hosted Microsoft 365 Copilot service. Reported scoring indicates low attack complexity, no user interaction requirement, and changed scope, with high impact across confidentiality, integrity, and availability.
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What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
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Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
9 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A deserialization of untrusted data vulnerability in Microsoft 365 Copilot that allows an authorized attacker to execute code over a network.
A critical insecure deserialization remote code execution vulnerability in Microsoft M365 Copilot that allows an authenticated low-privilege attacker to execute arbitrary code over the network.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.