CVE-2026-107587 Details
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.
A vulnerability exists in Progressive Robot hMailServer versions 6.3.2 through 6.3.5, related to improper certificate validation in the webmail S/MIME feature. This flaw allows a remote, unauthenticated attacker to manipulate S/MIME-encrypted emails. When a recipient opens a signed message, the webmail incorrectly retains the signer's certificate for future replies, regardless of the certificate's trust status. The certificate is stored under the first email address listed, rather than the actual sender's address, and alongside any existing certificates for that address. Consequently, replies are encrypted to all stored certificates, enabling an attacker with access to the private key of the intercepted certificate to decrypt the message.
Upgrade to hMailServer version 6.3.6, which addresses the certificate validation issue. After upgrading, review the S/MIME certificate list for each correspondent and remove any incorrect certificates. Instructions for upgrading are available in the hMailServer release notes.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Oct 8, 2026CISA-ADP
Assessed Oct 8, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6 | [email protected] | Release NotesVendor |
| https://gitlab.com/hmailserver/hmailserver/-/work_items/66 | [email protected] | ExploitIssue TrackingRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-295 | Improper Certificate Validation | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| Progressive Robot hMailServer | >= 6.3.2, <= 6.3.5 (semver) |
CPE
Remediation
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Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Oct 8, 2026 | CVE Modified | CISA-ADP |
| Oct 8, 2026 | New CVE Received | [email protected] |