Open-Xchange Dovecot Pro/Dovecot CE SMTP Command Interpretation injection

Summaryinfo

A vulnerability was found in Open-Xchange Dovecot Pro and Dovecot CE. It has been classified as problematic. The impacted element is an unknown function of the component SMTP Command Interpretation. This manipulation causes injection. This vulnerability is tracked as CVE-2026-33604. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability classified as problematic was found in Open-Xchange Dovecot Pro and Dovecot CE (unknown version). Affected by this vulnerability is an unknown code block of the component SMTP Command Interpretation. The manipulation with an unknown input leads to a injection vulnerability. The CWE definition for the vulnerability is CWE-74. The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component. As an impact it is known to affect integrity. The summary by CVE is:

An attacker that can get Dovecot to relay a message, for example through Sieve redirect or submission relay, can use a crafted line ending in the message body to bypass the outbound protection that prevents message content from being interpreted as SMTP commands. A downstream mail server that hasn't yet fixed the SMTP smuggling vulnerability can be tricked into treating part of the message body as new SMTP commands, allowing injection of spoofed email. This is the same vulnerability class as CVE-2023-51764 and CVE-2023-51766. Where you control the receiving mail servers, ensure they reject bare carriage returns in message data. Update to non-vulnerable version. No publicly available exploits are known.

It is possible to read the advisory at documentation.open-xchange.com. This vulnerability is known as CVE-2026-33604 since 03/23/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 08/28/2026). The attack technique deployed by this issue is T1055 according to MITRE ATT&CK.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-3076). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

• Open Source Dovecot

Productinfo

Type

• Mail Server Software

Vendor

• Open-Xchange

Name

• Dovecot CE
• Dovecot Pro

License

• open-source

Website

• Vendor: https://www.open-xchange.com/

CPE 2.3info

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CPE 2.2info

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Entryinfo

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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