TL;DR · 30-second read
The Short Version
Hackers backed by the Russian state have spent about a year breaking into organizations through a popular email system called Zimbra, according to the United States National Security Agency and 26 partner agencies across 16 countries.
The worrying part: nobody has to click anything. Simply opening a booby-trapped email on an out-of-date system lets the attackers copy the last three months of messages and the organization’s full staff contact list.
The fix is ordinary but urgent: install the software update, then check whether anything was already taken.
On July 23, 2026, the National Security Agency (NSA) said in a press release that it and 26 partner agencies from 16 countries had published a joint Cybersecurity Advisory titled “Russian State-Supported Cyber Actors Conduct Phishing Campaign Targeting Users of Zimbra Collaboration Suite.” The advisory attributes the activity to LAUNDRY BEAR, a Russian state-supported advanced persistent threat group, which has targeted Zimbra Collaboration Suite (ZCS) users across U.S. and allied government and commercial networks since July 2025.
The group uses a custom tool the agencies call “Ulej” to deliver an exploit that triggers automatically when a user views a malicious email in a vulnerable version of Zimbra’s webmail. The flaw, CVE-2025-66376, was a zero-day when first used and is still being exploited on unpatched servers. The exploit attempts to exfiltrate the organization’s email directory, the last 90 days of the victim’s communications, and other sensitive information.
Executive Summary
A coalition of intelligence and cybersecurity agencies spanning the Five Eyes and much of NATO Europe has put its name to a single warning: a Russian state-supported group has been quietly harvesting email from Zimbra servers for roughly a year, and it is still succeeding wherever administrators have not patched. The co-sealing list runs from the FBI and CISA to the UK’s National Cyber Security Centre, France’s ANSSI, both Dutch intelligence services, and agencies in Poland, Estonia, Finland, Sweden and Moldova.
What makes this advisory operationally important is the delivery mechanism. The exploit is “view-based”: it fires when a user opens the message in webmail, with no link to click and no attachment to run. That removes the human judgement that most phishing defenses rely on and turns the problem into one of patch management and network monitoring. For any organization that runs its own mail infrastructure, including data center, connectivity and cloud operators, the question is no longer whether staff can spot a suspicious email but whether the server was patched before the message arrived.
The advisory also documents what the exfiltration looks like on the network and lists indicators of compromise, the specific technical fingerprints defenders can search for, along with remediation steps. That matters because patching closes the door going forward but does nothing about mail that has already left.
When Viewing Is Enough, Training Stops Being the Control
Most organizations treat phishing as a people problem: teach staff not to click unfamiliar links or open unexpected attachments, and run simulated campaigns to measure progress. The exploit described in this advisory sidesteps that model entirely. According to the NSA, it “triggers automatically when a user views a malicious email within a vulnerable version of the webmail service.” A well-trained employee who opens a plausible-looking message to decide whether it is suspicious has already triggered it.
That shifts the controlling variable from user behavior to software version. On a patched Zimbra server, the message is inert; on an unpatched one, reading it is the compromise. The NSA states the exploit “is still used to successfully exploit ZCS instances that are still unpatched,” which tells defenders two things: the attackers are getting returns from this technique roughly a year after the campaign began in July 2025, and the population of vulnerable servers is large enough to keep them doing it. Awareness training remains useful against the wider phishing threat, but against this specific campaign the effective defense is patch speed, followed by hunting for signs of earlier theft.
The people most affected are administrators of self-managed mail systems. When email runs as a cloud service, the provider patches the server. When an organization runs Zimbra on its own hardware or virtual machines, that job falls to an internal team competing with every other maintenance priority, and a webmail server that “still works” is easy to defer.
What 90 Days of Mail and a Directory Are Worth to an Attacker
The exploit targets three things: the organization’s email directory, the last 90 days of the victim’s communications, and “other sensitive information.” Each has distinct value. The directory is a map of the organization: names, roles and addresses that make the next round of targeted phishing more convincing. Ninety days of mail captures current projects, vendor relationships, internal decisions and, frequently, credentials or configuration details that people send to one another despite policy.
For operators of physical and digital infrastructure, the stakes are concrete. Email is where maintenance windows are scheduled, where network change requests are discussed, where customer contracts and site access arrangements are negotiated. A three-month window of that traffic from one well-placed mailbox can give an intelligence service a detailed view of how an operator runs and who it serves, without ever touching the operational network itself.
The directory theft also means the damage can compound. Contacts harvested from one victim become credible senders and plausible targets for the next, which is one reason a campaign of this kind can keep expanding across “U.S. and allied government and commercial networks,” as the release describes.
A 27-Agency Signal on Breadth and Priority
Joint advisories are common; one carrying the seals of 27 agencies across 16 countries is not routine. The list includes foreign intelligence services, military counterintelligence and financial authorities (the U.S. Department of the Treasury) alongside the civilian cyber agencies that usually issue these warnings. The release does not explain why each agency joined, and the breadth should not be over-read as a measure of damage. It does indicate that the activity has been observed, or is considered relevant, across a wide set of allied governments.
The advisory’s technical focus is also telling. The NSA says it “characterizes the network activity occurring during the exfiltration stage.” That is aimed at defenders who may already be compromised: an organization that patched in, say, the last few months still needs to know whether data left its network before then. Egress logs, proxy records and firewall data from the preceding year are the relevant evidence, and teams that do not retain those logs long enough will struggle to answer the question.
The Practical Sequence for Zimbra Operators
The advisory implies a clear order of work. First, confirm that every Zimbra instance, including forgotten test or regional servers, is on a version that addresses CVE-2025-66376. Second, search mail and network logs for the indicators of compromise the advisory lists. Third, if any match, follow the remediation steps in the full report and assume the directory and recent mail of affected users are in hostile hands.
That third step has consequences beyond IT. If 90 days of correspondence has been exfiltrated, legal, contractual and customer-notification questions follow. For infrastructure providers whose customers include government agencies or regulated industries, a confirmed compromise of internal mail may need to be treated as a customer-facing incident, not just an internal clean-up.
Background
Email servers have long been a favored target for state-backed intelligence operations because a single compromised mailbox can reveal an organization’s contacts, plans and internal discussions. Self-hosted webmail platforms such as Zimbra are especially exposed: they sit on the public internet by design, and keeping them patched depends entirely on the operator’s own team.
Joint advisories from the NSA, CISA, FBI and allied agencies are the main channel through which Western governments share technical detail about state-sponsored campaigns with the private sector. They typically include indicators of compromise and mitigation guidance so that organizations can check their own systems, and a large number of co-sealing agencies generally reflects broad concern among allied governments about the activity described. Source: NSA and Partners Alert Zimbra Collaboration Suite Users of a Russian State-Supported Phishing Campaign — National Security Agency press release announcing a joint advisory on LAUNDRY BEAR’s exploitation of CVE-2025-66376 in Zimbra webmail.Sources