CVE-2026-107577 Loop with Unreachable Exit Condition ('Infinite Loop') in hMailServer
Remote unauthenticated attackers can cause denial of service in hMailServer by sending crafted MIME messages that trigger infinite loops or excessive processing time.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-107577?
CVE-2026-107577 is a high-severity denial of service vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Inefficient algorithmic complexity and a non-terminating loop in the MIME processing of received messages in Progressive Robot hMailServer 6.0.0 through 6.3.5 allow a remote unauthenticated attacker to make the mail services unavailable by sending a message. Removing a MIME header parameter whose value is empty and directly followed by a semicolon (for example a Content-Disposition with 'filename=a.bat; filename=;') entered a loop that never terminates, holding a worker thread at full load until the server is restarted; this is reached when the attachment blocker renames a blocked attachment or a filename is set over the REST API. Separately, decoding a header field that holds many RFC 2047 encoded words of an encoding other than base64 or quoted-printable, removing a parameter with many RFC 2231 continuations, and deleting many header fields of one name each took time growing with the square of the message, on the small thread pools that serve IMAP, SMTP and POP3 connections, delivery and the REST API.
Weakness: CWE-835
Which versions are affected by CVE-2026-107577?
How do I fix CVE-2026-107577?
No fix has been published for CVE-2026-107577 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-107577 being exploited?
There is no known exploitation of CVE-2026-107577 in the wild and no public exploit code.
Sources
Also known as GHSA-q3hj-9493-685w.