Security readout for executives and security teams
Plain-English summary
CVE-2025-27915 lets a malicious calendar entry in email run script in a victim's Zimbra Classic Web Client session. The business risk is account misuse, email redirection, and data exposure. Although the CVSS score is medium, CISA lists it as known exploited, making remediation urgent for exposed Zimbra mail environments.
Executive priority
Treat this as urgent remediation for Zimbra mail systems. Known exploitation and the possibility of silent email redirection raise business impact beyond the medium CVSS score, especially for executives, finance, legal, and incident-response mailboxes.
Technical view
This is stored XSS in Zimbra Collaboration 9.0, 10.0, and 10.1 Classic Web Client ICS handling. Insufficient HTML sanitization allows embedded JavaScript in calendar content to execute when a user views the email. CVSS is 5.4 with network attack vector, low complexity, low privileges, and required user interaction.
Likely exposure
Organizations running Zimbra Collaboration 9.0, 10.0, or 10.1 with Classic Web Client enabled are the main concern. Exposure is higher where users receive external calendar invitations or ICS-bearing emails and where mail accounts have valuable access or sensitive messages.
Exploitation context
CISA KEV confirms known exploitation, and StrikeReady describes in-the-wild abuse. The source bundle does not provide complete campaign scale, affected customer counts, or a universal indicator set, so assume targeted or opportunistic risk until local evidence is checked.
Researcher notes
Evidence supports stored XSS via ICS HTML sanitization in Classic Web Client and known exploitation. Public sources identify fixed Zimbra release pages, but the supplied data does not establish broader product impact, exact exploit prevalence, or complete detection logic.
Mitigation direction
- Apply the relevant Zimbra security release: 10.1.5, 10.0.13, or 9.0.0 P44.
- Check Zimbra Security Center for any newer vendor guidance or superseding releases.
- Prioritize internet-facing and high-value mail environments before lower-risk systems.
- Review account filter rules for unauthorized forwarding or redirection.
- Increase monitoring for suspicious mailbox rule changes and unusual session activity.
Validation and detection
- Inventory Zimbra Collaboration versions and confirm Classic Web Client usage.
- Confirm patched builds match the relevant Zimbra release security notes.
- Review mailboxes for unexpected filters, forwarding rules, or delegation changes.
- Look for user reports tied to suspicious calendar invitation emails.
- Check logs for unusual account actions after ICS-bearing messages were viewed.
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-2025-27915 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
- Medium
- CVSS
- 5.4 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/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:L/UI:R/S:C/C:L/I:L/A:N2.32.7Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.4MediumVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://wiki.zimbra.com/wiki/Security_CenterCVE reference
- https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.5#Security_FixesCVE reference
- https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.13#Security_FixesCVE reference
- https://wiki.zimbra.com/wiki/Zimbra_Releases/9.0.0/P44#Security_FixesCVE reference
- https://strikeready.com/blog/0day-ics-attack-in-the-wild/CVE reference
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-27915CVE reference
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.