CVE-2026-73570: Synacor Zimbra Collaboration Suite (ZCS)

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

Yes, if you run Synacor Zimbra Collaboration Suite (ZCS). CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-08-21, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-08-24; treat that as the outer limit, not the target.
EPSS 71.7%, percentile 99: FIRST’s model estimates a 71.7% chance of exploitation activity in the next 30 days, higher than 99% of all scored CVEs (very high). EPSS is a probability, not a verdict.
Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
Editorial verdict: Check exposure. Zimbra CVE-2026-73570: Exploited SNMP Command Injection — If you run Zimbra below 10.1.20, check today whether the optional zimbra-snmp package is installed with SNMP notifications on; if it is, patch and hunt for web shells, because hundreds of such servers have been compromised.

What it is

A remote code execution vulnerability exists in Zimbra Collaboration (ZCS) before 10.1.20 when the optional zimbra-snmp package is installed and SNMP notifications are enabled. Due to improper sanitization of untrusted input during SNMP notification processing, an unauthenticated attacker can send specially crafted SMTP requests that may result in execution of arbitrary operating system commands as the Zimbra user.

CISA’s summary

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.

Weakness type: CWE-78.

Product: Synacor Zimbra Collaboration Suite (ZCS) · Assigned by: mitre · Published: 2026-08-13

Affected and fixed versions

Vendor	Product	Affected versions (per CVE record)
Zimbra	Collaboration	< 10.1.20

Severity scores

Scored by	CVSS	Score	Vector
mitre	3.1	8.9 High	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L`

Attack vector: network (remotely reachable)
Attack complexity: high (needs special conditions)
Privileges required: none (no login)
User interaction: none
Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

CISA KEV: added 2026-08-21; federal due date 2026-08-24. Known ransomware use: Unknown.
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.
CISA SSVC assessment: exploitation active, automatable no, technical impact total.
FIRST EPSS (model of 2026-10-21): 71.66% probability of exploitation activity in the next 30 days; percentile 99.

Timeline

2026-07-20 — erroneo.us brief: Zimbra CVE-2026-73570: Exploited SNMP Command Injection
2026-08-13 — CVE record published by mitre
2026-08-21 — Added to CISA’s Known Exploited Vulnerabilities catalog
2026-08-24 — CISA remediation deadline for US federal agencies
2026-08-24 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Other references from the CVE record and advisory

wiki.zimbra.com wiki.zimbra.com
moje.cert.pl moje.cert.pl

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