International alert spotlights Russia-linked attacks on Zimbra webmail

International alert spotlights Russia-linked attacks on Zimbra webmail

Russian state-aligned hackers have been compromising governmental and commercial organizations throughout the West through zero-click phishing emails, federal agencies in the U.S., U.K., Europe, Australia and New Zealand warned on Thursday.

The campaign, carried out by the advanced persistent threat (APT) group Laundry Bear, targets Zimbra Collaboration Suite’s webmail platform and exploits a vulnerability that was patched in November 2025.

According to the advisory, the hackers carried out “extensive” targeting of Ukrainian entities before training their sights on U.S. and NATO organizations — evidence of “an increasing trend within Russian cyber threat groups to target Ukrainian users first—both as a priority target and as a testbench for malicious cyber techniques before broader global deployment.”

“The covert and persistent nature of this activity, along with the absence of any known financial extortion, almost certainly indicates this group’s involvement in espionage activities with Russian government backing,” the agencies concluded.

Palo Alto Networks’ Unit 42, which also published a report Thursday on the campaign, said the hackers targeted the defense and transportation sectors, as well as financial organizations in NATO member states, Ukraine, Commonwealth of Independent States countries and Africa. In its own advisory, Proofpoint said the group had compromised “government, high science, and defense industrial base targets in the United States.”

Laundry Bear was first identified in May 2025 by Dutch intelligence agencies, which blamed the group for a series of hacks in the Netherlands, including on the national police. According to Microsoft, it has been active since at least 2024. Previous campaigns involved “unsophisticated” techniques, like password spraying and phishing attempts that required a recipient to click on a link.

Since at least July 2025, the group has been deploying a novel exploit against the CVE-2025-66376 vulnerability in which a malicious JavaScript payload is hidden in emails sent from previously compromised email accounts. The payload is executed immediately when the emails are opened.

According to the advisory, the hackers have attempted to exfiltrate the last 90 days of emails from a compromised account, passwords, contact lists, two-factor authentication tokens and other passcodes.

In March 2026, the cybersecurity firm Seqrite described a zero-click phishing campaign exploiting Zimbra webmail that compromised a Ukrainian maritime agency. They attributed the activity with medium confidence to the Russian APT known as Fancy Bear. Dutch intelligence said Laundry Bear’s tactics “overlap with the modus operandi” of Fancy Bear but that they are different actors.

Proofpoint researchers said the campaign reflects other activity in recent years from Russian and Belarusian hackers using cross-site scripting exploits “to pillage webmail servers.”

The government agencies implored organizations using the Zimbra webmail service to immediately patch their software and, if patching is not feasible, to direct employees to use a different mail client.