# CVE-2026-93633: Zimbra Collaboration Suite Briefcase CSS Sanitization Bypass via Non-ASCII Stylesheet Characters


- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/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-x7vx-vqqq-6frh

## What is CVE-2026-93633?

CVE-2026-93633 is a medium-severity vulnerability in Synacor Zimbra Collaboration Suite, published on 23 Oct 2026. 

### Official description

A CSS sanitization vulnerability in Zimbra Collaboration Suite (ZCS) allows an authenticated user with Briefcase access to publish a document that displays attacker-controlled content under the Zimbra origin. When processing a stylesheet containing non-ASCII characters, DefangFilter appends the final ASCII segment without sanitizing it. HTML stored as application/x-zimbra-doc can therefore retain CSS URL references that the normal sanitizer removes. An attacker can share a crafted document that loads external resources and displays a credential-collection form using Zimbra's own visual assets. Exploitation requires the victim to open the document in a browser that renders the content type inline; credential theft additionally requires form submission. ZCS 10.1.16 and 10.1.20 are affected.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-93633?

It affects 1 product.


Products: Synacor Zimbra Collaboration Suite.

## How do I fix CVE-2026-93633?

No fix has been published for CVE-2026-93633 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-93633 being exploited?

There is no known exploitation of CVE-2026-93633 in the wild and no public exploit code.

## Other vulnerabilities in Synacor Zimbra Collaboration Suite

- [CVE-2024-45519](https://insights.sbomify.com/CVE-2024-45519/): Synacor Zimbra Collaboration Suite (ZCS) Command Execution (critical 10.0, exploited in the wild)
- [CVE-2022-41352](https://insights.sbomify.com/CVE-2022-41352/): Synacor Zimbra Collaboration Suite (ZCS) Arbitrary File Upload (critical 9.8, exploited in the wild)
- [CVE-2022-37042](https://insights.sbomify.com/CVE-2022-37042/): Synacor Zimbra Collaboration Suite (ZCS) Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2022-27924](https://insights.sbomify.com/CVE-2022-27924/): Synacor Zimbra Collaboration Suite (ZCS) Command Injection (critical 9.8, exploited in the wild)
- [CVE-2020-7796](https://insights.sbomify.com/CVE-2020-7796/): Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93633 and fix it if it is affected.

What it is: CVE-2026-93633 is a medium-severity vulnerability in Synacor Zimbra Collaboration Suite, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-93633 in the wild and no public exploit code.

Affected product: Synacor 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-2026-93633/ (Markdown: https://insights.sbomify.com/CVE-2026-93633/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93633
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93633
- OSV: https://osv.dev/vulnerability/CVE-2026-93633

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93633/
Summaries are generated and may contain mistakes; the official description above is the record.