--- id: "CVE-2026-73570" kind: "vulnerability" aliases: ["CVE-2026-73570"] title: "synacor zimbra collaboration suite: A remote code execution vulnerability exists in Zimbra Collaboration (ZCS) before 10.1.20 when the optional\u2026" severity: "critical" cvss: 8.9 epss: null exploited: true status: "resolved" category: "vendor" products: [{"name": "Synacor Zimbra Collaboration Suite (ZCS)", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "Zimbra Collaboration Suite (ZCS)", "fixed": ["10.1.20"], "affected": "< 10.1.20 (only with zimbra-snmp installed and SNMP notifications enabled)", "ecosystem": "vendor"}, {"name": "synacor zimbra collaboration suite", "fixed": ["10.1.20"], "affected": "< 10.1.20", "ecosystem": "vendor"}] ecosystems: ["vendor"] tags: ["email", "exploited", "rce", "self-hosted", "smtp", "unauthenticated", "vendor", "zimbra"] not_affected_if: ["managed-hosting", "snmp-notifications-disabled", "zimbra-snmp-not-installed"] published_at: "2026-08-13T16:19:06+00:00" first_seen_at: "2026-10-23T19:11:51+00:00" updated_at: "2026-10-23T23:44:52+00:00" sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-73570", "first_seen_at": "2026-10-23T19:11:51+00:00"}, {"source": "analyst", "url": null, "first_seen_at": "2026-10-23T21:32:01+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-73570", "first_seen_at": "2026-10-23T23:44:52+00:00"}] --- # synacor zimbra collaboration suite: A remote code execution vulnerability exists in Zimbra Collaboration (ZCS) before 10.1.20 when the optional… Unauthenticated OS command injection in Zimbra's SNMP notification path. A malformed SMTP RCPT TO address is logged to /var/log/zimbra.log. Swatchdog matches it as a 'Service status change' line and passes it to a backticked shell call in dosnmp, so commands run as the zimbra user. It needs the optional zimbra-snmp package with SNMP notifications enabled. It is exploited in the wild (CISA KEV, Aug 21 2026) and public PoCs exist. Microsoft saw web shells, root escalation, credential theft and lateral movement across Zimbra clusters. Fixed in ZCS 10.1.20 (Jul 20 2026); the CVE was disclosed Aug 13. _Summary, check and fix written by a model from the sources; labelled as such._ ## Affected - vendor:Synacor Zimbra Collaboration Suite (ZCS) affected ? fixed ? - vendor:Zimbra Collaboration Suite (ZCS) affected < 10.1.20 (only with zimbra-snmp installed and SNMP notifications enabled) fixed 10.1.20 - vendor:synacor zimbra collaboration suite affected < 10.1.20 fixed 10.1.20 ## How to check Version: run 'zmcontrol -v' as the zimbra user; anything below 10.1.20 is affected. SNMP exposure: check whether the package is installed ('dpkg -l zimbra-snmp' or 'rpm -q zimbra-snmp'). Check whether the service is enabled ('su - zimbra -c "zmprov gs $(zmhostname) zimbraServiceEnabled"' and look for snmp). Check whether /opt/zimbra/conf/swatchrc.in still has the unpatched dosnmp backtick call. Only port 25 or 587 SMTP reachability is needed to deliver the trigger. Hunt for exploitation: a shell child of the swatchdog Perl process that is not snmptrap, odd zimbra.log lines containing 'Service status change' with $( or backticks, unexpected JSP files under the Zimbra webroot, and a zimlog.service systemd unit. Also look for a NOPASSWD entry for zimbra and /tmp/s named pipes (Microsoft's IOCs). ## Fix Upgrade to ZCS 10.1.20 or later (10.1.21 is out as of Sep 24 2026). If you cannot upgrade immediately, Zimbra's June 26 2026 interim mitigation (reported by a third party; I did not read Zimbra's own advisory) is to stop swatch and disable the snmp service on MTA and Logger nodes: 'zmswatchctl stop' and 'zmprov ms $(zmhostname) -zimbraServiceEnabled snmp'. If you were exposed after Jul 20, assume compromise: check for web shells, rotate the Zimbra service credentials from zmlocalconfig -s, rotate zimbraPreAuthKey and zimbraAuthTokenKey, and review cluster nodes reachable via the zimbra SSH identity. ## Timeline - 2026-10-23T19:11:51+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-73570 - 2026-10-23T21:32:01+00:00 analyst — Primary source: Zimbra 10.1.20 release notes and blog (fix confirmed; the vendor does not name the CVE ID there). The affected range comes from the NVD/GHSA text and Tenable ('before 10.1.20'). Exploitation is confirmed by CISA KEV, Microsoft (Sep 30) and CERT Polska. Elastic notes that several public PoCs fail because the payload does not match swatchdog, so a failed test does not mean a patched server. Not read: Zimbra's June 26 advisory itself (the mitigation came from a secondary source), and whether older 9.x/10.0 branches are affected (unknown). Severity left as critical because of KEV and active exploitation (the CVSS is 8.9). Did not search X or Bluesky for discussion. - 2026-10-23T23:44:52+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-73570 ## Documents - [advisory] Zimbra blog: Patch Release 10.1.20 (permanent SNMP fix) https://blog.zimbra.com/2026/07/patch-release-update-zimbra-10-1-20/ - [describes] Microsoft: exploitation of CVE-2026-73570 https://www.microsoft.com/en-us/security/blog/2026/09/30/unauthenticated-command-injection-on-internet-facing-mail-servers-tracking-cve-2026-73570/ - [fix] Zimbra 10.1.20 release notes https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.20 - [mentions] CSA Singapore alert AL-2026-109 https://www.csa.gov.sg/alerts-and-advisories/alerts/al-2026-109/ - [mitigation] Zimbra SNMP swatchdog mitigation (June 2026 interim steps) https://www.excellent.co.id/news/informasi-keamanan-mengatasi-celah-keamanan-snmp-swatchdog-di-zimbra-severity-s1/ - [poc] Elastic: how CVE-2026-73570 works, PoC notes, detection https://www.elastic.co/security-labs/threat-command/command-injection-zimbra-cve-2026-73570 ## From the sources 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. CISA required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines. --- _Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_