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CVE-2026-26164 is a high-severity information disclosure vulnerability affecting Microsoft 365 Copilot Business Chat. The flaw is caused by improper neutralization of special elements in output used by a downstream component, classified as CWE-74. Crafted attacker-controlled input can influence Copilot output that is subsequently consumed by another component, creating an injection condition that can cause sensitive information to be disclosed back to the attacker over the network. The vulnerability is remotely reachable, requires no authentication, no privileges, and no user interaction. Microsoft assessed the issue with CVSS v3.1 vector AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N and a base score of 7.5. The issue was a cloud service vulnerability remediated server-side by Microsoft.
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What an attacker gets, and what they’ve been doing with it.
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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.
8 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A critical information disclosure vulnerability in Microsoft 365 Copilot involving improper neutralization of special elements in output used by a downstream component.
A critical information disclosure vulnerability in M365 Copilot caused by improper neutralization of special elements in output used by a downstream component, allowing unauthorized network-based disclosure of information.
An information disclosure vulnerability in Microsoft 365 Copilot Business Chat caused by improper neutralization of special elements in output used by a downstream component, allowing unauthenticated remote data extraction without user interaction.
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.