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CVE-2026-100741: hMailServer

Severity

9.8 (CRITICAL)

Vendor

PROGRESSIVE ROBOT LTD

Affected versions

6.0.0 through before 6.3.4

Fixed version

6.2.25

Patch status

Patched

Published

2026-09-27T08:16:26.813

Modified

2026-09-27T08:16:26.813

Why it matters

This matters because the affected product may be exploitable without valid credentials. Internet-facing deployments should be reviewed first.

Recommended admin actions

• Prioritize validation immediately due to critical CVSS severity.
• Compare installed versions against the affected version range in the advisory.
• Treat internet-facing systems as higher priority.

Technical summary

Eval injection in the JScript event-script dispatcher in Progressive Robot Ltd's hMailServer, versions 6.0.0 through 6.3.3 on Windows, allows a remote, unauthenticated attacker to run arbitrary JScript inside the hMailServer service process, with the privileges of the service account, via a password containing a backslash followed by an apostrophe, sent in any logon (SMTP AUTH, POP3, IMAP) that names an existing, active account. Exploitation requires a non-default configuration: event scripting enabled (off by default), the script language set to JScript (the default is VBScript), and an OnClientValidatePassword handler defined in the event script. The server wrote event values into the handler call as JScript string literals, escaping the apostrophe but not the backslash, so such a value closes the literal and the rest of it is parsed as script. The same flaw is reachable by a remote POP3 server through the message UID it returns, where an OnExternalAccountDownload handler is defined, and by a remote SMTP server through the error reply it rejects a delivery with, where an OnDeliveryFailed handler is defined. Before 6.2.25 the injected script can create any COM object, and from 6.2.25 it can with the default ScriptAllowedObjects value of '*'; WScript.Shell among them gives command execution as the service account. VBScript event scripts and the Linux builds of Progressive Robot Ltd's hMailServer are not affected.

View the official NVD record for CVE-2026-100741

CVE data is sourced from NVD/CNA records and optional enrichment. Validate against the vendor advisory before taking production action.