Microsoft finally patches critical one-click Copilot vulnerability, almost eight months after learning of it

“This is the pattern CISOs must internalize: in agentic systems, the malicious action and the legitimate action are the same action with different intent, which collapses the entire signature-and-anomaly detection model that enterprise security has been built on for twenty years,” Mahapatra said. “CoSnitch is serious, but its defining property is that nothing was broken. Three chained flaws: an autorun URL parameter firing a prompt with no click, OAuth connector abuse reading full Gmail bodies rather than metadata, and persistent memory poisoning through web summarization, and every one is Copilot doing exactly what it was designed to do.”

Mahapatra added that the third element of the CoSnitch flaw is the most troubling.

“The memory-poisoning component is the one being undersold, and it is the most dangerous. A single summarized webpage writes attacker instructions into Copilot’s persistent memory, and that memory survives password changes, session revocation, and device re-enrollment,” he said. “Every standard incident response step leaves the injection intact. The attacker needs no persistent infrastructure after the initial write, because every future session runs under attacker-controlled context, recorded only in a memory settings UI almost no user has opened.”

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AndyC

Andy Curtis is an award-winning security consultant, researcher and public speaker. He has been working in the computer security industry since the early 1990s, having been employed by state and federal government, leading healthcare and banking providers across three continents. He has given talks about computer security for some of the world’s largest companies, worked with law enforcement agencies on investigations into hacking groups, and is a regular voice on TV and radio explaining IT security threats.

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