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CVE-2026-93643 – Unauthenticated RCE via Path Traversal – Zimbra Collaboration Suite (ZCS) before 10

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Summary

CVE-2026-93643 is a critical unauthenticated path-traversal vulnerability in Zimbra Collaboration Suite (ZCS) that allows remote attackers to write arbitrary files and execute commands as the zimbra user. The flaw resides in the OnlyOffice/Document Editing integration and is triggered through unsigned save fields when handling public Briefcase documents. It carries a CVSS v3.1 base score of 9.8 (Critical) and requires no authentication or user interaction to exploit.

Technical details

  • Root cause: insufficient validation and signature enforcement of "unsigned save fields" used by the OnlyOffice/Document Editing integration when saving edits to Briefcase documents, tracked as CWE-22 (Path Traversal) combined with CWE-863 (Incorrect Authorization).
  • Trigger condition: the target ZCS instance must have OnlyOffice/Document Editing enabled and have an existing, publicly accessible Briefcase document available.
  • Attack vector: an unauthenticated remote attacker accesses the public Briefcase document and manipulates the unsigned save fields to inject path-traversal sequences into the server-side file write operation, allowing files to be written outside the intended directory.
  • Impact: arbitrary file write can be leveraged to execute commands as the zimbra service account, resulting in full compromise of confidentiality, integrity, and availability of the mail server.

Affected software

  • Zimbra Collaboration Suite (ZCS) — all versions prior to 10.1.21 (where OnlyOffice/Document Editing integration is enabled)
  • Fixed in ZCS 10.1.21 and later

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade Zimbra Collaboration Suite to version 10.1.21 or later, where this issue is fixed.
  • If patching is not immediately possible:
    • Disable the OnlyOffice/Document Editing integration until the upgrade can be applied.
    • Restrict or remove public sharing of Briefcase documents where feasible.
    • Restrict network access to the Zimbra web interface to trusted IP ranges.
    • Monitor Zimbra server logs and file system activity for unexpected writes or command execution by the zimbra user.

References

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