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CVE-2026-107568

MEDIUMCVSS 6.5/10EPSS 0.24%

Last modified

CVE-2026-107568 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. Missing authorization in the Sieve notify action (6.2.22 through 6.3.6) and in the mail-rule Reply action (6.0.0 through 6.3.6) of Progressive Robot hMailServer allows an authenticated user to send mail through the server as any address. A Sieve notify sends a notification message, and its :from tag names the sender; the server set the notification's From header to that :from as the script wrote it, without checking that the address belongs to the account - the check that the Sieve vacation action applies to its own :from, and that the server applies to the sender of mail queued over COM or sent from the webmail. EPSS estimates a 0.24% chance of exploitation in the next 30 days.

Description

Missing authorization in the Sieve notify action (6.2.22 through 6.3.6) and in the mail-rule Reply action (6.0.0 through 6.3.6) of Progressive Robot hMailServer allows an authenticated user to send mail through the server as any address. A Sieve notify sends a notification message, and its :from tag names the sender; the server set the notification's From header to that :from as the script wrote it, without checking that the address belongs to the account - the check that the Sieve vacation action applies to its own :from, and that the server applies to the sender of mail queued over COM or sent from the webmail. An account that can store a Sieve script (over ManageSieve, the REST API's self-service filter, or the administration interface) could therefore have the server send a notification from any address, on this server or anywhere; and where the claimed address is at a domain the server hosts with DKIM signing enabled, the server signed the notification with that domain's DKIM key, because it signs by the From header's domain, producing forged mail aligned to pass the domain's DMARC policy. The notify action and this behaviour were introduced in 6.2.22. In the mail-rule engine, a rule's Reply was likewise sent from whatever address the action named, whoever the rule belonged to, so that an account acting on its own rules over COM, a domain administrator, or an API key confined to a domain (over the REST API from 6.3.4) could have a domain's or an account's rule reply from any address, signed, where that address is at a domain the server hosts with DKIM signing enabled, with that domain's key.

Metrics

CVSS 3.1
6.5/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

EPSS Probability
0.24%

14.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
Progressive Robot LtdhMailServer>= 6.0.0, <= 6.3.6

References

Timeline

Published
Last Modified
Status
Deferred

Frequently Asked Questions

What is CVE-2026-107568?
Missing authorization in the Sieve notify action (6.2.22 through 6.3.6) and in the mail-rule Reply action (6.0.0 through 6.3.6) of Progressive Robot hMailServer allows an authenticated user to send mail through the server as any address. A Sieve notify sends a notification message, and its :from tag names the sender; the server set the notification's From header to that :from as the script wrote it, without checking that the address belongs to the account - the check that the Sieve vacation action applies to its own :from, and that the server applies to the sender of mail queued over COM or sent from the webmail. An account that can store a Sieve script (over ManageSieve, the REST API's self-service filter, or the administration interface) could therefore have the server send a notification from any address, on this server or anywhere; and where the claimed address is at a domain the server hosts with DKIM signing enabled, the server signed the notification with that domain's DKIM key, because it signs by the From header's domain, producing forged mail aligned to pass the domain's DMARC policy. The notify action and this behaviour were introduced in 6.2.22. In the mail-rule engine, a rule's Reply was likewise sent from whatever address the action named, whoever the rule belonged to, so that an account acting on its own rules over COM, a domain administrator, or an API key confined to a domain (over the REST API from 6.3.4) could have a domain's or an account's rule reply from any address, signed, where that address is at a domain the server hosts with DKIM signing enabled, with that domain's key.
How severe is CVE-2026-107568?
CVE-2026-107568 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 0.24% probability of exploitation in the next 30 days.
How do I fix CVE-2026-107568?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST