# CVE-2026-115786: Zimbra Collaboration Suite mailbox quota depletion

Source: https://junglewise.ai/threats/cve-2026-115786-a-mailbox-quota-accounting-vulnerability-in-zimbra-collaboration  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-23. Updated: 2026-10-23  
License: CC BY 4.0 with a link back

CVE-2026-115786 · Severity: medium · CVSS 6.5 · Published 2026-10-23

Zimbra Collaboration Suite is an enterprise email and collaboration platform. An authenticated user can exploit a flaw in how the system tracks shared document storage to consume another user's mailbox quota, potentially preventing them from receiving new email and using other storage-dependent features. This requires only a valid account on the system, not administrative access.

Technologies: [Zimbra Collaboration Suite](https://junglewise.ai/threats/technologies/collaboration). Vendors: [Zimbra](https://junglewise.ai/threats/vendors/zimbra).

## Quick answers

**Is CVE-2026-115786 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-115786 being exploited in the wild.

**How severe is CVE-2026-115786?** Medium severity, with a CVSS score of 6.5, published 23 October 2026.

**Which products and versions are affected?** Zimbra Collaboration Suite 10.1.16, 10.1.20.

**Is there a fix for CVE-2026-115786?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-115786 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-115786?** Check whether you run Zimbra Collaboration Suite at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a quota-accounting logic error in document sharing: when a document is shared with a recipient, the document size is charged to the recipient's mailbox quota, but when the share is revoked, the mailbox-wide quota charge is not reversed while folder counters are. An authenticated user can repeatedly share and revoke a document to an arbitrary target, causing the quota to accumulate charges without leaving visible shared-file records. This allows denial of service against any user's mailbox on systems with finite quotas.

## Affected products

- Zimbra Collaboration Suite 10.1.16, 10.1.20

## Timeline

- 2026-10-23: disclosed

## References

- [https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories](https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories)
- [https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/](https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/)

## Related threats

- [Zimbra Collaboration Suite local privilege escalation in dnscache](https://junglewise.ai/threats/cve-2026-93640-a-local-privilege-escalation-vulnerability-in-the-optional)
- [Zimbra Collaboration Suite authorization bypass in Zimlet configuration](https://junglewise.ai/threats/cve-2026-93639-a-missing-authorization-vulnerability-in-zimbra-collaboration)
- [Zimbra Collaboration Suite reflected cross-site scripting in login](https://junglewise.ai/threats/cve-2026-93638-a-reflected-cross-site-scripting-vulnerability-in-the-login-page)
- [Zimbra Collaboration Suite LDAP filter injection](https://junglewise.ai/threats/cve-2026-93636-an-ldap-filter-injection-vulnerability-in-zimbra-collaboration)
- [Zimbra Collaboration Suite cross-account authorization bypass in FileSharedWithMeRequest](https://junglewise.ai/threats/cve-2026-93634-a-cross-account-authorization-vulnerability-in-zimbra)