Kiteworks recommends server shutdown pending possible attack

Sophos • September 25, 2026

emerged that Kiteworks (formerly Acellion) emailed customers that law enforcement alerted them an “imminent” cyberattack on Kiteworks systems, possibly caused by exploitation of a zero-day vulnerability. Kiteworks reportedly advised customers to shut down servers between 02:00 and 08:00 UTC on September 26, if not sooner, as a “

Counter Threat Unit™ (CTU) researchers recommend that Kiteworks customers follow the guidance in the vendor’s email or Kiteworks directly.

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This article is one source in a clustered incident — the cluster page carries the summary, timeline and every other outlet covering it.

Kiteworks Issues Urgent Shutdown Advisory Amid Zero-Day Threat Kiteworks has alerted its customers to shut down their servers due to credible threat intelligence indicating an imminent cyberattack exploiting a zero-day vulnerability. The advisory, which applies globally, recommends a six-hour shutdown window starting September 26, 2026. This precautionary measure comes as Kiteworks, formerly known as Accellion, has faced scrutiny following previous breaches linked to vulnerabilities in its file transfer application. The exact nature of the vulnerability remains undisclosed, and no CVE has been assigned yet. Security experts have expressed concern over the unusual nature of the advisory, as it suggests a serious threat without confirmed details. The company has confirmed that all known vulnerabilities have been patched in its latest software release, version 9.5.1. Kiteworks serves a wide range of industries, including healthcare and finance, raising the stakes for potential data breaches. 30 sources 72

Kiteworks recommends server shutdown pending possible attack

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