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CVE-2026-93630— Zimbra Collaboration Suite Email HTML Sanitizer Bypass via Hostname Canonicalization

Quick assessment

Affected

Zimbra Zimbra Collaboration Suite

Exploitation

No confirmed in-the-wild exploitation; assess based on exposure

Recommended action

Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Zimbra Collaboration Suite（ZCS）的电子邮件 HTML 清理器中存在一个主机名规范化漏洞，使得未认证的发送方能够绕过针对指向 Zimbra 主机的表单的限制。DefangFilter 和 OWASP ActionAttributePolicy 在浏览器执行 URL 规范化之前，会比较表单的 action 属性中的主机名与请求的主机名。因此，经过百分号编码（percent-encoded）的主机名可能通过清理过程，而浏览器随后会将表单提交至正常的 Zimbra 源站，并携带收件人的身份认证

CVSS 4.3 · Medium Updated Oct 23, 2026

Possible ATT&CK Techniques 3 AI

T1055.001 · Dynamic-link Library Injection T1190 · Exploit Public-Facing Application T1566.002 · Spearphishing Link

Affected Version Matrix 1

Vendor	Product	Version Range	Status
Zimbra	Zimbra Collaboration Suite	`< 10.1.21`	affected

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Vulnerability Information

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Vulnerability Title

Zimbra Collaboration Suite Email HTML Sanitizer Bypass via Hostname Canonicalization

Source: CVE Program / CVE List V5

Vulnerability Description

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.

Source: CVE Program / CVE List V5

CVSS Information

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Source: CVE Program / CVE List V5

Vulnerability Type

不正确的行为次序：规范化之前验证

Source: CVE Program / CVE List V5

Affected Products

Vendor	Product	Affected Versions	CPE	Subscribe
Zimbra	Zimbra Collaboration Suite	0 ~ 10.1.21	-

II. Public POCs for CVE-2026-93630

#	POC Description	Source Link	Shenlong Link

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III. Intelligence Information for CVE-2026-93630

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Vendor Advisories for CVE-2026-93630 (1)

Zimbra Security Advisories - Zimbra :: Tech Center vendor-advisory

Other References for CVE-2026-93630 (1)

https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/ related

https://www.cve.org/CVERecord?id=CVE-2026-93630

Same Patch Batch · Zimbra · 2026-10-23 · 17 CVEs total

CVE-2026-10632	8.7 HIGH	Zimbra Collaboration Suite Classic Web Client Reflected Cross-Site Scripting via Document
CVE-2026-50053	8.7 HIGH	Zimbra Collaboration Suite RestFilter Request Attribute Override via Unauthenticated URL P
CVE-2026-93639	8.7 HIGH	Zimbra Collaboration Suite Missing Authorization in ConfigureZimlet Enables Delegated Admi
CVE-2026-93640	7.8 HIGH	Zimbra Collaboration Suite Local Privilege Escalation via Unrestricted zmunbound Sudo Conf
CVE-2026-50056	7.8 HIGH	Zimbra Collaboration Suite Local Privilege Escalation via zmmailboxdmgr JVM Argument Injec
CVE-2026-50057	7.8 HIGH	Zimbra Collaboration Suite Local Privilege Escalation via Unrestricted Postfix Sudo Permis
CVE-2026-93631	7.1 HIGH	Zimbra Collaboration Suite OAuth Extension Cross-Site Request Forgery Enables Account Link
CVE-2026-115786	6.5 MEDIUM	Zimbra Collaboration Suite Shared-File Mailbox Quota Accounting Error Enables Quota Exhaus
CVE-2026-93638	6.1 MEDIUM	Zimbra Collaboration Suite Pre-Authentication Reflected Cross-Site Scripting via Login Pag
CVE-2026-93633	5.4 MEDIUM	Zimbra Collaboration Suite Briefcase CSS Sanitization Bypass via Non-ASCII Stylesheet Char
CVE-2026-93629	5.3 MEDIUM	Zimbra Collaboration Suite Calendar Processing Authentication Bypass via Forged iCalendar
CVE-2026-93627	5.3 MEDIUM	Zimbra Collaboration Suite Calendar Processing Authentication Bypass via Forged iCalendar
CVE-2026-93628	5.3 MEDIUM	Zimbra Collaboration Suite Calendar Processing Authentication Bypass via Forged iCalendar
CVE-2026-93634	4.3 MEDIUM	Zimbra Collaboration Suite Cross-Account Authorization Bypass via Forged Shared-File Recor
CVE-2026-93636	4.3 MEDIUM	Zimbra Collaboration Suite LDAP Filter Injection via Calendar Resource Attribute Name
CVE-2026-115785	4.3 MEDIUM	Zimbra Collaboration Suite Data Source Test SMTP Command Injection via Unsanitized Email A

IV. Related Vulnerabilities

Same product: Zimbra Collaboration Suite

Same vendor: Zimbra

Same weakness: CWE-180

V. Comments for CVE-2026-93630

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Goal Reached Thanks to every supporter — we hit 100%!

CVE-2026-93630— Zimbra Collaboration Suite Email HTML Sanitizer Bypass via Hostname Canonicalization

Quick assessment

Possible ATT&CK Techniques 3 AI

Affected Version Matrix 1

I. Basic Information for CVE-2026-93630

Vulnerability Information

Vulnerability Title

Vulnerability Description

CVSS Information

Vulnerability Type

Affected Products

II. Public POCs for CVE-2026-93630

III. Intelligence Information for CVE-2026-93630

Vendor Advisories for CVE-2026-93630 (1)

Other References for CVE-2026-93630 (1)

Same Patch Batch · Zimbra · 2026-10-23 · 17 CVEs total

IV. Related Vulnerabilities

V. Comments for CVE-2026-93630

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