Threat actors have weaponized a now-patched security flaw in Zimbra Collaboration Suite (ZCS) to deploy web shells and access mailbox data, according to findings from the Microsoft Security Research team. The attack exploits CVE-2026-73570 (CVSS score: 8.9), an unauthenticated operating system command injection flaw that can lead to remote code execution when Simple Network Management Protocol

Microsoft Threat Intelligence examines CVE-2026-73570 exploitation in Zimbra, including observed attack paths, detection opportunities, and mitigation guidance. The post Unauthenticated command injection on internet-facing mail servers: tracking CVE-2026-73570 appeared first on Microsoft Security Blog .

Here’s an overview of some of last week’s most interesting news, articles, interviews and videos: Unpatched Zimbra servers are falling to CVE-2026-73570 attacks At least 274 internet-facing Zimbra instances have been compromised by unknown attackers via CVE-2026-73570, the Shadowserver Foundation shared on Monday. AI supply chain risk is showing up in developer workflows first In this Help Net Security interview, Dr. Jaushin Lee, CEO of Zentera Systems, discusses where AI supply chain risk shows up. … More → The post Week in review: Compromised Zimbra servers, previously patched Citrix NetScaler flaw exploited appeared first on Help Net Security .

More Than 8,000 Unpatched Instances Remain Exposed to CVE-2026-73570 Attackers have compromised at least 267 Zimbra installations through a likely CVE-2026-73570 campaign, while more than 8,000 unpatched servers remain exposed to unauthenticated remote code execution that can give attackers access to mail data and system resources.

At least 274 internet-facing Zimbra instances have been compromised by unknown attackers via CVE-2026-73570, the Shadowserver Foundation shared on Monday. About CVE-2026-73570 Zimbra Collaboration Suite (ZCS) is a communication and collaboration platform popular with organizations that need to have control over their data or can’t afford a pricy alternative service like Microsoft 365 or Google Workspace. CVE-2026-73570 is a code injection flaw Synacor patched in ZCS v10.1.20, released on July 20, 2026. The vulnerability was … More → The post Unpatched Zimbra servers are falling to CVE-2026-73570 attacks appeared first on Help Net Security .

CISA has issued a three-day deadline for agencies to patch a Zimbra security vulnerability, CVE-2026-73570, which allows full takeover of a user's communications.

U.S. Cybersecurity and Infrastructure Security Agency (CISA) adds Zimbra Collaboration Suite (ZCS) flaw to its Known Exploited Vulnerabilities catalog. The U.S. Cybersecurity and Infrastructure Security Agency (CISA) added the Zimbra Collaboration Suite (ZCS) flaw CVE-2026-73570 to its Known Exploited Vulnerabilities (KEV) catalog. CERT Polska, Poland’s national computer emergency response team, confirmed this week that threat actors […]

CISA has added one new vulnerability to its Known Exploited Vulnerabilities (KEV) Catalog , based on evidence of active exploitation.   CVE-2026-73570 Zimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability This type of vulnerability is a frequent attack vector for malicious cyber actors and poses significant risks to the federal enterprise. Binding Operational Directive (BOD) 26-04: Prioritizing Security Updates Based on Risk establishes vulnerability management requirements for Federal Civilian Executive Branch (FCEB) agencies. BOD 26-04 reinforces the importance of the KEV Catalog and requires federal agencies to prioritize rapid remediation of high-risk vulnerabilities, specifically those identified by Common Vulnerabilities and Exposures (CVEs) listed in CISA’s KEV Catalog on publicly exposed assets that grant total control of the asset post-exploitation, while deferring action for lower-risk vulnerabilities. BOD 26-04 further establishes basic expectations for when agencies must check whether threat actors compromised the system before the patch was applied. While BOD 26-04 applies only to FCEB agencies, CISA encourages all organizations to adopt risk-based vulnerability management and prioritize remediation of KEV Catalog vulnerabilities . CISA will continue to add vulnerabilities to the catalog that meet the specified criteria . Aware of an exploited vulnerability not currently listed in the KEV Catalog? Submit it for potential ad...

CERT Polska confirmed active exploitation of CVE-2026-73570, a critical unauthenticated RCE in Zimbra Collaboration Suite patched on July 20. CERT Polska, Poland’s national computer emergency response team, confirmed this week that threat actors are actively exploiting a critical vulnerability in Zimbra Collaboration Suite tracked as CVE-2026-73570. The flaw allows unauthenticated remote code execution and was […]

Zimbra Collaboration Suite (ZCS) contains an OS command injection vulnerability which could allow an unauthenticated attacker to send specially crafted SMTP requests that may result in execution of arbitrary operating system commands as the Zimbra user.

A now-patched security flaw impacting Zimbra Collaboration (ZCS) has come under active exploitation in the wild, according to the Polish Computer Emergency Response Team (CERT Polska). The vulnerability in question is CVE-2026-73570 (CVSS score: 8.9), which refers to a case of command injection that can lead to remote code execution. "A remote code execution vulnerability exists in Zimbra

Proofpoint is releasing this report in coordination with NSA and FBI’s JSAC reporting about TA488/Void Blizzard, which can be found here. This is part 1 of a 2-part blog series Proofpoint is publishing about Russian espionage actors using half-click exploits to target government webmail servers. Read part 2 about TA458 here. Threat Research would like to thank the Proofpoint Cloudmark Authority team. Key Findings Proofpoint uncovered that Russia-aligned threat actor TA488 (Void Blizzard, Laundry Bear) was exploiting a previously unknown vulnerability against Zimbra mailservers for at least five months during 2025, until the issue was patched with CVE-2025-66376. After successful exploitation, TA488 established persistent access to the systems and exfiltrated emails from the targeted users. The campaigns targeted Ukrainian government entities, as well as government, high science, and defense industrial base targets in the United States. TA488 is one of several Russian-aligned groups Proofpoint tracks that are using half-click exploits to target email servers, a stealthy method that only requires a user to open the email for the exploit code to execute. Overview In the last three years, the threat intelligence community has reported cyber espionage activity from Russian and Belarussian threat actors targeting webmail appliances with cross-site scripting (XSS) vulnerabilities. Actors such as TA422 (Sofacy, Forest Blizzard, Fancy Bear, APT28), TA473...