Volexity is seeing active in-the-wild exploitation of multiple Microsoft Exchange vulnerabilities used to steal e-mail and compromise networks. In January 2021, through its Network Security Monitoring service, Volexity detected anomalous activity from two of its customers' Microsoft Exchange servers. This vulnerability is remotely exploitable and does not require authentication of any kind, nor does it require any special knowledge or access to a target environment. Additionally, Volexity is providing alternative mitigations that may be used by defenders to assist in securing their Microsoft Exchange instances. This vulnerability has been confirmed to exist within the latest version of Exchange 2016 on a fully patched Windows Server 2016 server. Volexity also confirmed the vulnerability exists in Exchange 2019 but has not tested against a fully patched version, although it believes they are vulnerable. There are two methods to download e-mail with this vulnerability, depending on the way that Microsoft Exchange has been configured. In the case where a single server is being used to provide the Exchange service, Volexity believes the attacker must know the targeted user’s domain security identifier (SID) in order to access their mailbox. Further other notable User-Agent entries tied to tools used for post-exploitation access to webshells. Network Indicators - Attacker IPs . Volexity has observed numerous IP addresses leveraged by the attackers to exploit the vulnerabilities described in this blog