# CVE-2026-33603: Security feature bypass in OX Dovecot Pro

> Attackers can bypass SCRAM TLS channel binding via crafted base64 exchanges, enabling man-in-the-middle eavesdropping on Dovecot client communications.

- **Severity:** Medium 6.8 (`CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 May 2026
- **Updated:** 12 May 2026
- **Also known as:** ALPINE-CVE-2026-33603, AZL-86802, DEBIAN-CVE-2026-33603, GHSA-gxj9-f8v6-q8h3, UBUNTU-CVE-2026-33603

## What is CVE-2026-33603?

CVE-2026-33603 is a medium-severity vulnerability in Dovecot Dovecot, published on 12 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Attacker can use a specially crafted base64 exchange between Dovecot and Client to fake SCRAM TLS channel binding. This requires that the attacker is able to position itself between Dovecot and the client connection. If successful, the attacker can eavesdrop communications between Dovecot and client as MITM proxy. Install fixed version. No publicly available exploits are known.

Weakness: CWE-99 (Improper Control of Resource Identifiers)

## Which versions are affected by CVE-2026-33603?

It affects 2 products.


Products: Dovecot Dovecot, Open-Xchange Dovecot.

## How do I fix CVE-2026-33603?

Upgrade to a fixed version.

## Is CVE-2026-33603 being exploited?

There is no known exploitation of CVE-2026-33603 in the wild and no public exploit code.

## Other vulnerabilities in Dovecot Dovecot

- [CVE-2026-24031](https://insights.sbomify.com/CVE-2026-24031/): Auth bypass in OX Dovecot Pro (high 7.7)
- [CVE-2025-59032](https://insights.sbomify.com/CVE-2025-59032/): Denial of service in OX Dovecot Pro (high 7.5)
- [CVE-2026-27858](https://insights.sbomify.com/CVE-2026-27858/): Denial of service in OX Dovecot Pro (high 7.5)
- [CVE-2021-29157](https://insights.sbomify.com/CVE-2021-29157/): Path traversal in n/a (high 7.5)
- [CVE-2020-10957](https://insights.sbomify.com/CVE-2020-10957/): Null dereference in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33603 and fix it if it is affected.

What it is: CVE-2026-33603 is a medium-severity vulnerability in Dovecot Dovecot, published on 12 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-33603 in the wild and no public exploit code.

Affected product: Dovecot Dovecot. 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-2026-33603/ (Markdown: https://insights.sbomify.com/CVE-2026-33603/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33603
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33603
- OSV: https://osv.dev/vulnerability/CVE-2026-33603

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33603/
Summaries are generated and may contain mistakes; the official description above is the record.