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CVE-2026-26129 is an unauthenticated information disclosure vulnerability in Microsoft 365 Copilot Business Chat. The flaw is described as improper neutralization of special elements in an AI-assisted processing context, with reporting indicating prompt-boundary or delimiter-handling failures that can cause passive input to be interpreted as instructions by downstream model or orchestration components. In practice, this can lead the service to retrieve or expose sensitive data from the user’s organizational work context, including Microsoft Graph-connected content such as email, collaboration messages, and documents. The vulnerability is network exploitable, requires no privileges, and does not require user interaction. Microsoft rated the issue Critical with CVSS 3.1 base score 7.5 and stated it was remediated at the service layer.
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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.
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Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
11 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A critical information disclosure vulnerability affecting Microsoft 365 Copilot and Copilot Chat in Microsoft Edge, mentioned only in related content.
A critical information disclosure vulnerability in Microsoft 365 Copilot Business Chat caused by 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, allowing an unauthorized remote attacker to disclose information over the network.
An unauthenticated information disclosure vulnerability in Microsoft 365 Copilot Business Chat caused by improper neutralization of special elements / prompt boundary failures, potentially allowing remote leakage of sensitive organizational data from Microsoft Graph-connected content.
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.