CVE-2026-126621: Progressive Robot hMailServer 6.0.0-B1 through 6.3.7 on Windows hands OpenSSL the names of its own TLS files - the listeners' certificates, chains, private keys

Progressive Robot hMailServer 6.0.0-B1 through 6.3.7 on Windows hands OpenSSL the names of its own TLS files - the listeners' certificates, chains, private keys

Progressive Robot hMailServer 6.0.0-B1 through 6.3.7 on Windows hands OpenSSL the names of its own TLS files - the listeners' certificates, chains, private keys and Diffie-Hellman parameters, a port's client-certificate CA file (from 6.2.19), the object store's CA file (from 6.3.4) and the ACME client's keys and certificates - as Latin-1 bytes, which on code page 1252 are the code page's own for U+00A0 to U+00FF, and OpenSSL's file opening on Windows reads a name as UTF-8 first and opens the file at that reading when it is there, or creates it there when its folder is. When every byte of a configured name outside ASCII also reads as UTF-8 - for example U+00C3 U+00A9, the bytes C3 A9, which are U+00E9 in UTF-8 - the server used the file at that other name whenever one was there, which allows a local attacker who can create that file or its folder but cannot change the configured one, as any user can by default beside a file an administrator keeps under ProgramData, to have a port that logs on by client certificate (from 6.2.25) accept certificates from a certificate authority of the attacker's own and so sign in over the network as any mailbox without its password; to have the serve

Description from the National Vulnerability Database, published by cve@gitlab.com

What it means for a small business

If your business uses hMailServer, install the vendor's update. If you're not sure whether you use it, ask whoever manages your computers.

How likely is an attack? The Exploit Prediction Scoring System, run by FIRST (the global association of security response teams), puts the odds of this one being exploited in the next 30 days at 0.17%, higher than 6% of CVEs. That’s low, but low isn’t zero, and the odds jump the day someone publishes an exploit. Scored November 15, 2026, updated daily.

Check your own setup

Website check: reads what your site runs from the outside (WordPress version, plugins it can see, old server software) and matches it against this database.
Server check: what your web server says about itself, and whether that version has known flaws.

Sources

Part of the Huttenlocher Technologies vulnerability database, refreshed twice a day from CISA and the NVD. The title, category and plain-language guidance are ours; check the linked record before acting on a detail. This is general guidance, not a review of your systems.

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