CVE-2026-107579 Details
Description
Inefficient algorithmic complexity in the bounce and complaint processing of Progressive Robot hMailServer 6.3.4 and 6.3.5 allows a remote unauthenticated attacker to stop mail delivery by sending messages, when bounce processing or complaint processing is enabled or a mailing list is managed by the server (none is by default). The readers of incoming delivery status notifications (RFC 3464) and abuse feedback reports (RFC 5965) removed the blank lines at the start of the returned headers part two bytes at a time, copying the rest of the part each time, so their work grew with the square of the number of blank lines. A message shaped like such a report, whose headers part begins with a very large number of blank lines within the reader's 2 MB limit, keeps a delivery thread busy for over a minute while it is delivered, and a few such messages a minute keep every delivery thread busy.
A denial-of-service vulnerability has been identified in Progressive Robot hMailServer versions 6.3.4 and 6.3.5. The issue arises from an inefficient algorithmic complexity in handling bounce and complaint processing. When these features are enabled, or if a mailing list is managed by the server, a remote unauthenticated attacker can disrupt mail delivery by sending messages that exploit this flaw. The vulnerability takes advantage of the server's handling of incoming delivery status notifications and abuse feedback reports, which process blank lines in a way that causes the processing time to increase quadratically with the number of blank lines. This leads to significant delays in message delivery, effectively stalling the server's mail processing capabilities.
Users are advised to upgrade to hMailServer version 6.3.6, which addresses this vulnerability. Instructions for upgrading are available in the release notes for version 6.3.6.
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/70 | [email protected] | ExploitIssue TrackingRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-407 | Inefficient Algorithmic Complexity | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| Progressive Robot hMailServer | 6.3.4 (semver) 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] |