Zimbra Collaboration Suite up to 10.1.21 Calendar Processing improper authorization

Summaryinfo

A vulnerability classified as problematic has been found in Zimbra Collaboration Suite up to 10.1.21. Affected by this issue is some unknown functionality of the component Calendar Processing. The manipulation leads to improper authorization. This vulnerability is documented as CVE-2026-93628. The attack can be initiated remotely. There is not any exploit available.

Detailsinfo

A vulnerability was found in Zimbra Collaboration Suite up to 10.1.21 and classified as problematic. This issue affects some unknown processing of the component Calendar Processing. The manipulation with an unknown input leads to a improper authorization vulnerability. Using CWE to declare the problem leads to CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. Impacted is integrity. The summary by CVE is:

An attendee authentication vulnerability in the email calendar processing of Zimbra Collaboration Suite (ZCS) allows an unauthenticated sender to forge another attendee's response to an existing meeting. Zimbra passes a null sender identity when processing iCalendar REPLY components, causing the attendee authorization filter to be skipped. An attacker who knows the meeting UID, organizer address and attendee address can send a non-outdated reply that changes the attendee's participation status in the organizer's calendar. The change occurs automatically during delivery without organizer or attendee interaction. ZCS 10.1.16 and 10.1.21 are affected.

The advisory is shared at wiki.zimbra.com. The identification of this vulnerability is CVE-2026-93628 since 09/18/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 10/23/2026). MITRE ATT&CK project uses the attack technique T1548.002 for this issue.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Groupware Software

Vendor

• Zimbra

Name

• Collaboration Suite

Version

• 10.1.0
• 10.1.1
• 10.1.2
• 10.1.3
• 10.1.4
• 10.1.5
• 10.1.6
• 10.1.7
• 10.1.8
• 10.1.9
• 10.1.10
• 10.1.11
• 10.1.12
• 10.1.13
• 10.1.14
• 10.1.15
• 10.1.16
• 10.1.17
• 10.1.18
• 10.1.19
• 10.1.20
• 10.1.21

CPE 2.3info

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CPE 2.2info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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