Microsoft has announced that up to 92% of all stand-alone Exchange servers have been patched, following a mass data breach by Chinese state-sponsored Hafnium cybercrime group.
A mass attack on zero-day Exchange servers through four security vulnerabilities was identified and exploited by Hafnium in early March. Those with at risk servers, according to Microsoft VP Tom Burt, are recognised as 400,000 on-premise Exchange servers belonging to multiple government and corporate data centres including defence contractors, schools and other entities globally.
Consequently, the ProxyLogon security fixes released on 2nd March have mitigated this number significantly with 92% of Exchange servers now protected under the new patches. Nevertheless, Microsoft states that around 32,000 servers remained unpatched and vulnerable to Hafnium cybercrime including theft of confidential sensitive data together with installation of ransomware and ‘corrupted web shells’, such as China Chopper, allowing unrestricted external access to the unpatched Exchange servers.
These security fixes are in conjunction with Microsoft’s Exchange on-premises mitigation tool (EOMT) which installs defender scripts and dependency downloads whilst automatically running the Safety Scanner; troubleshooting any identified problems on the Exchange servers.
However, the patches do not protect servers that have already been compromised from further exploitation, therefore Microsoft has advised that organisations administrators scan their stand-alone networks for potentially installed malicious software and scripts in addition to the scans of EOMT.
The attacks themselves have raised questions over the security maintenance of in-house email servers and adds weight to the growing adoption of cloud-based internet email.