China Chopper Web shells are an older threat causing new problems for many organizations targeted in ongoing attacks against vulnerable Microsoft Exchange Servers worldwide.

Since Microsoft patched a series of Exchange Server zero-days on March 2, what had previously been "limited and targeted" attacks quickly became a global issue as attackers weaponized the critical flaws. Security companies tracking the activity, including FireEye and Red Canary, noticed China Chopper Web shells played a consistent role in their observed attack patterns.

Less than two weeks after the flaws were disclosed, the DHS' Cybersecurity and Infrastructure Security Agency (CISA) updated its guidance on the vulnerabilities to include seven China Chopper Web shells connected to successful attacks against vulnerable Exchange Servers. 

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