CVE-2025-66376Known exploitationNetwork attack vector

Stored XSS via CSS @import directives

Published Jan 5, 2026 · Updated Jan 5, 2026

Stored XSS in Zimbra Collaboration 10.0 before 10.0.18 and 10.1 before 10.1.13 allows attackers to run script via crafted HTML email. The Classic UI renders stored HTML email without neutralizing CSS @import directives, allowing attacker-controlled imports to trigger script execution. Exploitation requires the crafted message to be rendered in Classic UI; the script then runs in the recipient's authenticated webmail context.

CVSS severity7.2
High
EPSS probability19.56%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in Zimbra Collaboration 10.0 before 10.0.18 and 10.1 before 10.1.13 allows attackers to run script via crafted HTML email. The Classic UI renders stored HTML email without neutralizing CSS @import directives, allowing attacker-controlled imports to trigger script execution. Exploitation requires the crafted message to be rendered in Classic UI; the script then runs in the recipient's authenticated webmail context.

The record

CVE
CVE-2025-66376
Published
Jan 5, 2026
Updated
Jan 5, 2026
Vendor
Zimbra
Product
Zimbra Collaboration
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 5, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 5, 2026Record updatedLatest update available in the CVE record.
  3. Mar 18, 2026Exploitation reportedCISA Known Exploited Vulnerabilities Catalog listing

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.0 <10.0.18
  2. Affected versionversion=10.1 <10.1.13

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Zimbra · Zimbra Collaborationversion=10.0 <10.0.18; version=10.1 <10.1.13

Published CVSS scores

6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
7.2MITRECVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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