CVE-2026-107567
7.5HighPublished 19 Oct 2026 · NVD status: Received · AI triage by gemini-3.8-flash
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
- Impact
- High impact on integrity
- Weakness
- CWE-348
Impact
Remote unauthenticated attackers can spoof email that passes DKIM and DMARC verification using your hosted domain keys. They only need to send inbound mail with a forged From header that triggers an automated outbound forward, alias, rule, or distribution list.
Root cause
The server signs every message with the DKIM key matching the From header on its initial delivery pass without verifying sender authentication or message origin.
Affected systems
Progressive Robot hMailServer 6.0.0 through 6.3.6
CVSS v3.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Fix & remediation
Upgrade to hMailServer 6.3.7 or later. As an interim workaround, disable DKIM signing on hosted domains that forward, alias, or route messages to external addresses.
AI-suggested. Run it in staging first and check it against the vendor advisory. Why?
NVD description
Use of a less trusted source in the DKIM signing of Progressive Robot hMailServer 6.0.0 through 6.3.6 allows a remote unauthenticated attacker to have mail they write signed with the DKIM key of a domain the server hosts, so that it passes DKIM and DMARC for that domain at other receivers. With DKIM signing enabled for a hosted domain, the server signed every message on its first delivery pass as the domain named in its From header, before local delivery, whatever the message's origin and without checking that its sender had authenticated. A sender anywhere could therefore send the server, as ordinary inbound mail, a message whose From is any address at such a domain, and the server signed it with that domain's key. Every copy the server then sent on to an address outside carried a valid signature aligned with the forged From, whatever the domain's DMARC policy: an account's forward, a mail rule's forward or copy, a Sieve redirect, an alias or distribution list with an outside member, the mirror copy, a managed-list or journal copy, or a message released from quarantine. A signed copy can also be re-sent to other recipients while the domain's key is unchanged. Exploitation needs DKIM signing to be enabled for the hosted domain (it is off until configured) and, for the forgery to leave the server, a forward, alias, list or rule that carries the domain's mail to an outside address. The signer likewise signed a message submitted over authenticated SMTP as whatever hosted domain its From header named, a header authenticated SMTP does not hold to the submitting account, so that an account of one hosted domain could have mail written in the name of another hosted domain signed with that domain's key; this mattered where the server holds signed-in senders to their own envelope addresses (SmtpAuthenticatedSenderCheck, off by default), as the signature was then the remaining way for such mail to pass the other domain's DMARC policy.