Description
Inefficient algorithmic complexity and a non-terminating loop in the MIME processing of received messages in Progressive Robot hMailServer 6.0.0 through 6.3.5 allow a remote unauthenticated attacker to make the mail services unavailable by sending a message. Removing a MIME header parameter whose value is empty and directly followed by a semicolon (for example a Content-Disposition with 'filename=a.bat; filename=;') entered a loop that never terminates, holding a worker thread at full load until the server is restarted; this is reached when the attachment blocker renames a blocked attachment or a filename is set over the REST API. Separately, decoding a header field that holds many RFC 2047 encoded words of an encoding other than base64 or quoted-printable, removing a parameter with many RFC 2231 continuations, and deleting many header fields of one name each took time growing with the square of the message, on the small thread pools that serve IMAP, SMTP and POP3 connections, delivery and the REST API.
Published: 2026-10-08
Score: 7.5 High
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

Vendor Solution

Upgrade to hMailServer 6.3.6, which removes a MIME parameter and deletes header fields in a single pass and searches an encoded word's terminator only for a decodable word. Until then: lower the maximum message size (which bounds the quadratic paths but not the non-terminating one), and restart the service to end a hung thread.

Tracking

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Advisories

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History

Thu, 08 Oct 2026 15:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Thu, 08 Oct 2026 12:00:00 +0000

Type Values Removed Values Added
Description Inefficient algorithmic complexity and a non-terminating loop in the MIME processing of received messages in Progressive Robot hMailServer 6.0.0 through 6.3.5 allow a remote unauthenticated attacker to make the mail services unavailable by sending a message. Removing a MIME header parameter whose value is empty and directly followed by a semicolon (for example a Content-Disposition with 'filename=a.bat; filename=;') entered a loop that never terminates, holding a worker thread at full load until the server is restarted; this is reached when the attachment blocker renames a blocked attachment or a filename is set over the REST API. Separately, decoding a header field that holds many RFC 2047 encoded words of an encoding other than base64 or quoted-printable, removing a parameter with many RFC 2231 continuations, and deleting many header fields of one name each took time growing with the square of the message, on the small thread pools that serve IMAP, SMTP and POP3 connections, delivery and the REST API.
Title Loop with Unreachable Exit Condition ('Infinite Loop') in hMailServer
Weaknesses CWE-835
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}


Subscriptions

No data.

cve-icon MITRE

Status: PUBLISHED

Assigner: GitLab

Published:

Updated: 2026-10-08T14:17:33.868Z

Reserved: 2026-10-08T10:51:50.638Z

Link: CVE-2026-107577

cve-icon Vulnrichment

Updated: 2026-10-08T14:17:29.516Z

cve-icon NVD

Status : Received

Published: 2026-10-08T12:17:15.630

Modified: 2026-10-08T15:17:43.943

Link: CVE-2026-107577

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-08T14:00:05Z

Weaknesses
  • CWE-835

    Loop with Unreachable Exit Condition ('Infinite Loop')