Zimbra Collaboration Suite Classic Web Client stored XSS (view-based/zero-click) exploited by Russian actor LAUNDRY BEAR; CVSS 7.2 (MITRE)/6.1 (NVD); CISA KEV; patched ZCS 10.0.18/10.1.13

Adversaries may upload, install, or otherwise set up capabilities that can be used during targeting. To support their operations, an adversary may need to take capabilities they developed (Develop Capabilities) or obtained (Obtain Capabilities) and stage them on infrastructure under their control. These capabilities may be staged on infrastructure that was previously purchased/rented by the adversary (Acquire Infrastructure) or was otherwise compromised by them (Compromise Infrastructure). Capabilities may also be staged on web services, such as GitHub or Pastebin, or on Platform-as-a-Service (PaaS) offerings that enable users to easily provision applications.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may send phishing messages to gain access to victim systems. All forms of phishing are electronically delivered social engineering. Phishing can be targeted, known as spearphishing. In spearphishing, a specific individual, company, or industry will be targeted by the adversary. More generally, adversaries can conduct non-targeted phishing, such as in mass malware spam campaigns.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may abuse various implementations of JavaScript for execution. JavaScript (JS) is a platform-independent scripting language (compiled just-in-time at runtime) commonly associated with scripts in webpages, though JS can be executed in runtime environments outside the browser.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may exploit software vulnerabilities in client applications to execute code. Vulnerabilities can exist in software due to unsecure coding practices that can lead to unanticipated behavior. Adversaries can take advantage of certain vulnerabilities through targeted exploitation for the purpose of arbitrary code execution. Oftentimes the most valuable exploits to an offensive toolkit are those that can be used to obtain code execution on a remote system because they can be used to gain access to that system. Users will expect to see files related to the applications they commonly used to do work, so they are a useful target for exploit research and development because of their high utility.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may manipulate accounts to maintain and/or elevate access to victim systems. Account manipulation may consist of any action that preserves or modifies adversary access to a compromised account, such as modifying credentials or permission groups. These actions could also include account activity designed to subvert security policies, such as performing iterative password updates to bypass password duration policies and preserve the life of compromised credentials.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may disable or modify multi-factor authentication (MFA) mechanisms to enable persistent access to compromised accounts.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may manipulate accounts to maintain and/or elevate access to victim systems. Account manipulation may consist of any action that preserves or modifies adversary access to a compromised account, such as modifying credentials or permission groups. These actions could also include account activity designed to subvert security policies, such as performing iterative password updates to bypass password duration policies and preserve the life of compromised credentials.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may smuggle data and files past content filters by hiding malicious payloads inside of seemingly benign SVG files. SVGs, or Scalable Vector Graphics, are vector-based image files constructed using XML. As such, they can legitimately include `<script>` tags that enable adversaries to include malicious JavaScript payloads. However, SVGs may appear less suspicious to users than other types of executable files, as they are often treated as image files.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may disable or modify multi-factor authentication (MFA) mechanisms to enable persistent access to compromised accounts.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

An adversary may steal web application or service session cookies and use them to gain access to web applications or Internet services as an authenticated user without needing credentials. Web applications and services often use session cookies as an authentication token after a user has authenticated to a website.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may disable or modify multi-factor authentication (MFA) mechanisms to enable persistent access to compromised accounts.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may attempt to get a listing of email addresses and accounts. Adversaries may try to dump Exchange address lists such as global address lists (GALs).

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may target an Exchange server, Office 365, or Google Workspace to collect sensitive information. Adversaries may leverage a user's credentials and interact directly with the Exchange server to acquire information from within a network. Adversaries may also access externally facing Exchange services, Office 365, or Google Workspace to access email using credentials or access tokens. Tools such as MailSniper can be used to automate searches for specific keywords.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may communicate using the Domain Name System (DNS) application layer protocol to avoid detection/network filtering by blending in with existing traffic. Commands to the remote system, and often the results of those commands, will be embedded within the protocol traffic between the client and server.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗

Adversaries may steal data by exfiltrating it over an un-encrypted network protocol other than that of the existing command and control channel. The data may also be sent to an alternate network location from the main command and control server.

Evidence: 2026-07-24/laundry-bear-zimbra-zero-click-cve-2025-66376 · ATT&CK page ↗