Security readout for executives and security teams
Plain-English summary
CVE-2025-66376 is a stored cross-site scripting issue in Zimbra Collaboration Classic UI. A malicious HTML email can abuse CSS @import handling so script-like content is stored and later affects users viewing mail. For organizations running affected ZCS 10 versions, this could expose user data or allow limited actions in the victim’s session.
Executive priority
Treat as a near-term patching priority for Zimbra mail systems. It is high severity, remotely reachable through email content, and affects user sessions. No active exploitation is confirmed in the provided sources, but mail platforms are high-value targets and should be updated promptly.
Technical view
Zimbra Collaboration 10.0 before 10.0.18 and 10.1 before 10.1.13 are affected. The flaw is CWE-79 stored XSS in Classic UI handling of HTML email CSS @import directives. CVSS 3.1 is 7.2, network reachable, low complexity, no privileges, scope changed, with low confidentiality and integrity impact.
Likely exposure
Exposure is limited to Zimbra Collaboration deployments on affected 10.0 or 10.1 releases where users access the Classic UI and receive HTML email. The source bundle does not identify other affected Zimbra versions or products.
Exploitation context
The CVE description supports an email-based stored XSS scenario. CISA KEV status in the provided bundle is false, so there is no source-grounded evidence here of active exploitation. No public exploit details are included in the provided sources.
Researcher notes
Key unknowns remain: the sources do not provide proof-of-concept details, exploit telemetry, or operational mitigations beyond fixed versions. Validation should focus on version confirmation, Classic UI exposure, and whether compensating mail sanitization controls exist, without relying on them as a vendor-stated fix.
Mitigation direction
- Upgrade Zimbra Collaboration 10.0 to 10.0.18 or later.
- Upgrade Zimbra Collaboration 10.1 to 10.1.13 or later.
- Review Zimbra security advisories for any additional vendor guidance.
- Prioritize systems with Classic UI enabled for user mail access.
Validation and detection
- Inventory Zimbra Collaboration servers and record exact version branches.
- Confirm whether any 10.0 systems are below 10.0.18.
- Confirm whether any 10.1 systems are below 10.1.13.
- Verify Classic UI availability and user exposure to HTML email.
- Check Zimbra release notes for the listed security fix.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-79: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2025-66376 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.2 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N3.92.7Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.2HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://wiki.zimbra.com/wiki/Zimbra_Security_AdvisoriesCVE reference
- https://wiki.zimbra.com/wiki/Security_CenterCVE reference
- https://wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_PolicyCVE reference
- https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13#Security_FixesCVE reference
- https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18#Security_FixesCVE reference
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376CVE reference · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.