# CVE-2026-93628: Zimbra Collaboration Suite Calendar Processing Authentication Bypass via Forged iCalendar REPLY Attendee Response


- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 23 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** GHSA-p5gv-qg22-w4gq

## What is CVE-2026-93628?

CVE-2026-93628 is a medium-severity vulnerability in Zimbra Collaboration Suite, published on 23 Oct 2026. 

### Official description

An attendee authentication vulnerability in the email calendar processing of Zimbra Collaboration Suite (ZCS) allows an unauthenticated sender to forge another attendee's response to an existing meeting. Zimbra passes a null sender identity when processing iCalendar REPLY components, causing the attendee authorization filter to be skipped. An attacker who knows the meeting UID, organizer address and attendee address can send a non-outdated reply that changes the attendee's participation status in the organizer's calendar. The change occurs automatically during delivery without organizer or attendee interaction. ZCS 10.1.16 and 10.1.21 are affected.

Weakness: CWE-290 (Authentication Bypass by Spoofing)

## Which versions are affected by CVE-2026-93628?


## How do I fix CVE-2026-93628?

No fix has been published for CVE-2026-93628 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-93628 being exploited?

There is no known exploitation of CVE-2026-93628 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93628 and fix it if it is affected.

What it is: CVE-2026-93628 is a medium-severity vulnerability in Zimbra Collaboration Suite, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-93628 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-2026-93628/ (Markdown: https://insights.sbomify.com/CVE-2026-93628/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93628
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93628
- OSV: https://osv.dev/vulnerability/CVE-2026-93628

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-93628/
Summaries are generated and may contain mistakes; the official description above is the record.