What is CVE-2026-115786?

CVE-2026-115786 is a medium-severity vulnerability in Zimbra Collaboration Suite, classified under Incorrect Calculation. CVSS score: 6.5/10. Published 2026-10-23.

How severe is CVE-2026-115786?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Zimbra Collaboration Suite

CVE-2026-115786

A mailbox quota-accounting vulnerability in Zimbra Collaboration Suite (ZCS) allows an authenticated user to consume another user’s mailbox quota by repeatedly sharing and revoking a document. Creation of the recipient’s shared-file record charges the document size to mailbox-wide usage. Revocation deletes the record and reverses its folder counters without reversing the mailbox-wide charge. Repeated normal share notifications therefore accumulate quota usage after the visible records are gone. On accounts with a finite quota, this can prevent incoming mail and other size-increasing operations without recipient interaction. The issue affects ZCS 10.1.16 and 10.1.20.

Published 2026-10-23 · last modified 2026-10-23.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Zimbra Collaboration Suite

Weakness classification (CWE)

CWE-682 — Incorrect Calculation

References

wiki.zimbra.com/wiki/Zimbra_Security_Advisories (vendor-advisory)
www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/ (related)

Frequently asked questions

What is CVE-2026-115786?: CVE-2026-115786 is a medium-severity vulnerability in Zimbra Collaboration Suite, classified under Incorrect Calculation. CVSS score: 6.5/10. Published 2026-10-23.
How severe is CVE-2026-115786?: Medium severity. CVSS v3 base score is 6.5 out of 10.