CVE-2026-107587 Improper Certificate Validation in hMailServer
An attacker can intercept S/MIME encrypted emails by exploiting improper certificate validation in hMailServer webmail, allowing unauthorized decryption of future replies.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-107587?
CVE-2026-107587 is a medium-severity vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Improper certificate validation in the webmail of Progressive Robot hMailServer 6.3.2 through 6.3.5 allows a remote unauthenticated attacker to have S/MIME-encrypted mail that the account later sends to another correspondent also encrypted to the attacker's key. When its recipient opened a signed message, the webmail kept the signer's certificate for encrypting replies whether or not the server found its chain trusted, under the first e-mail address the certificate listed rather than the message's From address, and beside any certificate already held for that address. Encrypted mail later sent from the webmail to that address was encrypted to every certificate held for it, so a holder of the kept certificate's key who obtains a copy of such a message can read it.
Weakness: CWE-295
Which versions are affected by CVE-2026-107587?
How do I fix CVE-2026-107587?
No fix has been published for CVE-2026-107587 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-107587 being exploited?
There is no known exploitation of CVE-2026-107587 in the wild and no public exploit code.
Sources
Also known as GHSA-j6xf-vpp5-5357.