Progressive Robot hMailServer up to 6.3.5 REST API Listener dns rebinding

Summaryinfo

A vulnerability categorized as critical has been discovered in Progressive Robot hMailServer up to 6.3.5. This affects an unknown part of the component REST API Listener. Executing a manipulation can lead to dns rebinding. This vulnerability appears as CVE-2026-104659. The attack may be performed from remote. There is no available exploit. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability has been found in Progressive Robot hMailServer up to 6.3.5 and classified as critical. This vulnerability affects an unknown functionality of the component REST API Listener. The manipulation with an unknown input leads to a dns rebinding vulnerability. The CWE definition for the vulnerability is CWE-350. The product performs reverse DNS resolution on an IP address to obtain the hostname and make a security decision, but it does not properly ensure that the IP address is truly associated with the hostname. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

Missing Host header validation and missing throttling of failed administrator sign-ins in the REST API listener of Progressive Robot hMailServer 6.0.0 through 6.3.5 allow a remote attacker to brute-force the server administrator's password through the administrator's own browser by DNS rebinding. The listener, which is off by default and bound to the loopback when enabled, answered requests whatever their Host header named, and a failed sign-in with the administrator's password from the loopback was neither auto-banned nor delayed. A web page whose host name the attacker rebinds to 127.0.0.1, opened in a browser on the server, can therefore send authenticated requests to the listener, read the answers and try administrator passwords at full speed until one is accepted, giving the attacker full administrative control of the mail server.

The advisory is available at gitlab.com. This vulnerability was named CVE-2026-104659 since 10/02/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Successful exploitation requires user interaction by the victim. The technical details are unknown and an exploit is not available. This vulnerability is assigned to T1583.002 by the MITRE ATT&CK project.

Upgrading to version 6.3.6 eliminates this vulnerability.

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Productinfo

Type

• Mail Server Software

Vendor

• Progressive Robot

Name

• hMailServer

Version

• 6.3.0
• 6.3.1
• 6.3.2
• 6.3.3
• 6.3.4
• 6.3.5

CPE 2.3info

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CPE 2.2info

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