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CVE-2026-26144 is a critical information disclosure vulnerability in Microsoft Excel caused by improper neutralization of input during web page generation, resulting in a cross-site scripting condition. The flaw can be triggered through malicious content embedded in an Excel file and, in environments where Copilot Agent mode is available, can cause the agent to process attacker-controlled input and exfiltrate spreadsheet data over the network through unintended egress. Reporting indicates the issue is notable because the vulnerable Excel/Copilot interaction can turn a traditional XSS condition into a zero-click-style data disclosure scenario once the malicious workbook is opened or processed, without requiring additional user approval prompts for the exfiltration step.
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A Microsoft Excel cross-site scripting vulnerability that, when chained with Copilot Agent mode, can enable silent data exfiltration from spreadsheets via the AI agent without user interaction.
An Excel information disclosure vulnerability that could leak data through Copilot.
Microsoft Excel information disclosure in Copilot Agent mode that could leak sensitive data across a network.
Unknown
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.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.