CVE-2026-93630
MediumCVSS 4.3Exploitation Probability (EPSS)
Low risk21th percentile - higher than 21% of all known CVEs
Summary
A hostname canonicalization vulnerability in the email HTML sanitizers of Zimbra Collaboration Suite allows an unauthenticated sender to bypass the restriction on forms that target the Zimbra host. DefangFilter and the OWASP ActionAttributePolicy compare the form-action hostname with the request hostname before browser URL canonicalization. A percent-encoded hostname can therefore survive sanitization while the browser submits the form to the normal Zimbra origin with the recipient's authentication cookie. This permits authenticated form requests from a crafted email after the recipient opens it in Classic and submits the form.
Risk Assessment
May lead to unauthorized actions on behalf of the victim if the endpoint does not require a CSRF token.
Recommendation
Update ZCS to a version later than 10.1.21 that fixes this vulnerability.
Other vulnerabilities in Zimbra Collaboration Suite
See all- CVE-2022-37042CriticalActively exploited
Zimbra Collaboration Suite (ZCS) 8.8.15 and 9.0 has mboximport functionality that receives a ZIP archive and extracts files from it. By bypassing authentication (i.e., not having an authtoken), an attacker can upload arbitrary files to the system, leading to directory traversal and remote code execution. NOTE: this issue exists because of an incomplete fix for CVE-2022-27925.
- CVE-2022-27925HighActively exploited
Zimbra Collaboration (aka ZCS) 8.8.15 and 9.0 has mboximport functionality that receives a ZIP archive and extracts files from it. An authenticated user with administrator rights has the ability to upload arbitrary files to the system, leading to directory traversal.
- CVE-2022-24682MediumActively exploited
The Calendar feature in Zimbra Collaboration Suite 8.8.x before 8.8.15 patch 30 allows an attacker to place HTML containing executable JavaScript inside element attributes. This markup becomes unescaped, causing arbitrary markup to be injected into the document.
- CVE-2019-9621HighActively exploited
An SSRF vulnerability in the ProxyServlet component of Zimbra Collaboration Suite. It allows an attacker to send requests from the server to internal resources.
- CVE-2018-6882MediumActively exploited
A cross-site scripting (XSS) vulnerability in ZmMailMsgView.getAttachmentLinkHtml in Zimbra Collaboration Suite (ZCS) before 8.7 Patch 1 and 8.8.x before 8.8.7. Remote attackers can inject arbitrary web script or HTML via a Content-Location header in an email attachment.
- CVE-2026-93638Medium
A reflected cross-site scripting vulnerability in the login page of Zimbra Collaboration Suite allows an unauthenticated attacker to execute JavaScript through the zrememberme parameter. A crafted relogin URL selects a two-factor error display that inserts the parameter into a hidden input attribute without HTML encoding. A victim who opens the URL receives attacker-controlled script and page content under the legitimate Zimbra origin, allowing credential capture through a replacement login form.
- CVE-2026-93636Medium
An LDAP filter injection vulnerability in Zimbra Collaboration Suite allows an authenticated user to query otherwise unreturned attributes of calendar resources through SearchCalendarResourcesRequest. Zimbra escapes search values but inserts the supplied attribute names directly into LDAP filter expressions without validation. 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.
- CVE-2026-93634Medium
A cross-account authorization vulnerability in Zimbra Collaboration Suite allows an authenticated user to insert forged shared-file records into another user's mailbox through FileSharedWithMeRequest. The request bypasses delegated-account authorization and accepts attacker-selected file metadata, owner identifiers and declared sizes without validating a corresponding document share. An attacker can plant entries attributed to another real local account without that account sharing a document. No victim interaction is required.
- CVE-2026-93633Medium
A CSS sanitization vulnerability in Zimbra Collaboration Suite allows an authenticated user with Briefcase access to publish a document that displays attacker-controlled content under the Zimbra origin. When processing a stylesheet containing non-ASCII characters, DefangFilter appends the final ASCII segment without sanitizing it. HTML stored as application/x-zimbra-doc can therefore retain CSS URL references that the normal sanitizer removes. An attacker can share a crafted document that loads external resources and displays a credential-collection form using Zimbra's own visual assets.
- CVE-2026-93629Medium
An organizer authentication vulnerability in Zimbra Collaboration Suite allows an unauthenticated email sender to insert calendar invitations attributed to another user. The email delivery path permits external invitations but does not verify that the message sender is authorized to use the iCalendar ORGANIZER identity. When automatic invitation insertion is enabled, a crafted REQUEST component creates an event containing attacker-selected meeting details and reminders under a forged organizer without recipient interaction. No corresponding event is created in the claimed organizer's calendar.
Original NVD description (English source)
A hostname canonicalization vulnerability in the email HTML sanitizers of Zimbra Collaboration Suite (ZCS) allows an unauthenticated sender to bypass the restriction on forms that target the Zimbra host. DefangFilter and the OWASP ActionAttributePolicy compare the form-action hostname with the request hostname before browser URL canonicalization. A percent-encoded hostname can therefore survive sanitization while the browser submits the form to the normal Zimbra origin with the recipient's authentication cookie. This permits authenticated form requests from a crafted email after the recipient opens it in Classic and submits the form. The issue is present in ZCS 10.1.16 and 10.1.21. It does not bypass an endpoint's CSRF-token checks; a state-changing attack additionally requires an endpoint that accepts the resulting request without that protection.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

