CVE-2026-93636 Zimbra CVE debrief

Who should care

Defenders responsible for Zimbra Collaboration Suite instances, particularly those with exposed calendar resources or sensitive internal information, should assess and remediate this vulnerability.

Why it matters

Defenders should prioritize verifying and remediating this vulnerability in Zimbra Collaboration Suite instances, particularly those with exposed calendar resources or sensitive internal information, to prevent potential exposure of internal mailbox hostnames and mail transport routes.

• Potential exposure of internal mailbox hostnames and mail transport routes
• Possible use of repeated matching queries to recover readable resource attributes
• Need for verification and remediation of affected Zimbra Collaboration Suite instances
• Potential impact on confidentiality due to LDAP filter injection

Technical summary

The vulnerability allows an authenticated user to inject LDAP filter expressions and recover readable resource attributes. Zimbra Collaboration Suite 10.1.16 and 10.1.21 are affected. The attack is restricted to calendar-resource objects and the LDAP service account's access rights. An attacker can inject additional conditions and use repeated matching queries to recover readable resource attributes such as internal mailbox hostnames and mail transport routes. Defenders should assess and remediate this vulnerability in Zimbra Collaboration Suite instances, particularly those with exposed calendar resources or sensitive internal information.

Defensive priority

Defenders should prioritize verifying and remediating this vulnerability in Zimbra Collaboration Suite instances, particularly those with exposed calendar resources or sensitive internal information.

Recommended defensive actions

• Verify Zimbra Collaboration Suite version and apply patches if necessary
• Restrict access to calendar resources and LDAP service accounts
• Monitor for suspicious SearchCalendarResourcesRequest activity
• Implement additional security measures to protect internal mailbox hostnames and mail transport routes
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE Program record and NVD vulnerability detail provide official information on the vulnerability. The source item and supplemental sources offer additional context and potential advisories. Defenders should verify Zimbra Collaboration Suite versions, assess exposure of calendar resources, and review internal mailbox hostnames and mail transport routes for potential impact. Evidence is limited to public sources and CVE Program records, which may not cover all affected systems or deployment specifics. Further verification is needed

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.