Business Email Compromise (BEC) operates on a familiar playbook. Threat actors breach a mailbox, silently monitor operations, map approval chains, and ultimately exploit that access to divert funds or exfiltrate sensitive assets.
This dynamic is central to our analysis as we kick off a series around Rapid7's collaborative research with Zimbra; upcoming installments will explore technical details and broader findings based within the Zimbra Collaboration Suite. Our investigation disrupted the traditional BEC model in unexpected ways. We uncovered over 50 vulnerabilities, and found that several allow attackers not just to observe environments, but to actively rewrite them by impersonating senders without credentials, controlling inbox visibility, and altering shared documents and calendars.
Business Email Compromise in action: Digital abuse of trust
None of this is theoretical for Zimbra. But don’t take my word for it, just ask Russia. CISA keeps putting Zimbra bugs into the Known Exploited Vulnerabilities catalog, and the last three years make the point on their own:
CVE-2024-45519, command injection in the postjournal service, unauthenticated command execution. Proofpoint saw attackers stuffing base64 payloads into CC fields on September 28, 2024. CISA added it to KEV on October 3.
CVE-2025-27915, stored XSS in the Classic Web Client, triggered by a crafted .ICS attachment. It is used as a zero-day against Brazilian military targets to steal mail and quietly set forwarding filters. It went into KEV in October, 2025.
CVE-2026-73570, unauthenticated command injection through SNMP notification handling. CISA added it on August 21 of this year and gave federal agencies three days. Shadowserver has been counting somewhere north of 260 compromised instances while hunting for exploitation artifacts.
Go back further and the pattern holds. Rapid7 tracked widespread exploitation of CVE-2022-27925 and CVE-2022-37042 in 2022, a path traversal chained with an authentication bypass that let attackers drop a JSP shell on a Zimbra server without credentials. Google's Threat Analysis Group later documented four separate threat groups working the same zero-day known as CVE-2023-37580. Each of these groups went after email, credentials, and authentication tokens. Attackers figured out a long time ago that the system sitting in the middle of everyone's communication is worth the effort. So when you find a set of bugs that let you write to that system instead of only reading from it, data theft stops being the interesting part.
Send an email as your CFO without ever touching their password, and you have the front half of a very convincing BEC. Keep control of the mailbox afterward and you have the back half, too. Here, the attacker has a strategic choice. They can delete the sent message to hide their tracks, effectively wiping the trail of the fraud OR they can choose to leave the message in the Sent Items folder. By doing so, they ensure the CFO sees 'evidence' of the email they supposedly sent, creating a gaslighting scenario where the victim is left questioning their own actions. Whether the attacker cleans up or leaves the trail, they are shaping the organization’s perception of reality. In the ensuing investigation, where Finance sees a sent request and the CFO sees no such activity, the organization is trapped in a conflict of evidence. At that point, BEC looks less like traditional fraud and more like a psychological operation.
Documents make it worse, as Zimbra is not just a mail server. The collaboration side holds the files employees actually use to make decisions. An attacker who can plant a fake HR memo or financial summary in an executive's enterprise drive, and make it look like it came from a peer they trust, is starting from a much better position than someone attaching a PDF to a cold email.
Say a document shows up from HR about a confidential restructuring, and a few days later an email from a trusted executive references it. Neither piece has to carry the whole deception, as each one props up the other.
Calendar warfare and manufactured enterprise reality
Then there is the thing I have started calling ‘calendar warfare.’ Meetings can be modified or deleted without generating the notification trail users expect to see. RSVP status can also be flipped. Maybe a key executive is changed from Accepted to Declined and leadership might reschedule, or move ahead without them, or read the whole thing as a deliberate opt-out.
It works in the other direction too. An "Emergency Board Meeting" lands on an executive's calendar with a believable organizer, a popup reminder, and a malicious Zoom link. When the reminder fires, the victim is not sizing up a suspicious email that arrived thirty seconds ago. They are joining a meeting that has been sitting in their calendar for two days. And the calendar is not some exotic attack surface nobody has thought of. If we look back at CVE-2025-27915, the delivery vehicle was a calendar invite.
Stack all of it together now – a financial document appears, a trusted executive emails about it, then a mandatory meeting shows up to discuss it. And the attacker still has the ability to clean up some of what gets left behind. Every artifact the victim checks lives inside a system they have no reason to question, and all of them tell the same fabricated story.
I keep coming back to the phrase 'manufactured enterprise reality'. I have touched on the idea in The Monday Brief, that attackers get to borrow whatever trust an organization has already extended to its own tooling. Zimbra makes it concrete. The platform supplies the credibility, so the attacker does not have to build any.
Collaboration suites quietly became systems of record. Email is the record of who said what. Calendars are the record of who agreed to be where. Classic BEC abuses the trust between two people. The scenario we’ve discussed here abuses the machinery those people use to decide who to trust in the first place. Once employees are making real business decisions off fabricated context, stealing data is the least of your problems.