# CVE-2026-115786: Zimbra Collaboration Suite Shared-File Mailbox Quota Accounting Error Enables Quota Exhaustion


- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 23 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** GHSA-w5xc-29c5-3j2h

## What is CVE-2026-115786?

CVE-2026-115786 is a medium-severity vulnerability in Zimbra Collaboration Suite, published on 23 Oct 2026. 

### Official description

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.

Weakness: CWE-682 (Incorrect Calculation)

## Which versions are affected by CVE-2026-115786?


## How do I fix CVE-2026-115786?

No fix has been published for CVE-2026-115786 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-115786 being exploited?

There is no known exploitation of CVE-2026-115786 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-115786 and fix it if it is affected.

What it is: CVE-2026-115786 is a medium-severity vulnerability in Zimbra Collaboration Suite, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-115786 in the wild and no public exploit code.

Affected product: Zimbra Collaboration Suite. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-115786/ (Markdown: https://insights.sbomify.com/CVE-2026-115786/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-115786
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-115786
- OSV: https://osv.dev/vulnerability/CVE-2026-115786

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-115786/
Summaries are generated and may contain mistakes; the official description above is the record.