CVE-2026-115786
MEDIUM 6.5A 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.
No known exploitation, public exploit, or elevated probability at this time. Track for changes.
Exploitation likelihood
0.4%chance of exploitation in 30 days · 31st percentile
Impact if exploited
6.5CVSS 3.1 · MEDIUM
- ConfidentialityNone
- IntegrityNone
- AvailabilityHigh
What an attacker needs
- ✓Access: Reachable over the network — no local access needed
- ⚠Privileges: Requires a low-privilege account
- ✓User interaction: No user interaction needed
- ✓Complexity: No special conditions — reliably repeatable
✓ lowers the bar for an attacker · ⚠ raises it
Proof of concept
No public PoC is currently catalogued.
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Data snapshot:
Weakness (CWE)
- CWE-682: Incorrect Calculation
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
References and research data (JSON)
All CVSS metrics
- MEDIUM 6.5 v3.1 · CNA Primary
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H - MEDIUM 6.5 v3.1 · NVD Secondary
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
References
Advisories
- https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories CVE record · rapid7 · Updated 2026-10-23T13:53:33.918Z
NVD · CVE-2026-115786 · Updated 2026-10-23T16:44:17.950 - https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-109080 EUVD · EUVD-2026-109080
Technical & other
- https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/ CVE record · rapid7 · Updated 2026-10-23T13:53:33.918Z
NVD · CVE-2026-115786 · Updated 2026-10-23T16:44:17.950