Description
Inefficient algorithmic complexity in the webmail's message view of the REST API in Progressive Robot hMailServer 6.3.2 through 6.3.5 allows a remote unauthenticated attacker to make the webmail, the administration console and the REST API unavailable by sending a message. The route that renders a received message's HTML replaced each reference to an embedded image in place, with work that grew with the square of the number of references, and wrote the image out for every reference while counting it against its size limit only once. A message whose HTML refers to one small embedded image a very large number of times, opened in the webmail by its recipient, therefore keeps one of the listener's four worker threads busy for minutes and makes it build a document of gigabytes, so that a few such messages leave the HTTP listener unable to answer anybody.
Published: 2026-10-08
Score: 6.5 Medium
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, in which the route reads a message's HTML once to find the images it names and once to write them, and writes at most 24 MB of inlined images in all, every reference counted. Until then: lower the maximum message size, which bounds the cost (it grows with the square of the HTML's size); leave the webmail's offline store off so that only an opened message triggers it; or keep the REST listener off (RestApiPort 0, the default).

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History

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

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Thu, 08 Oct 2026 13:30:00 +0000

Type Values Removed Values Added
First Time appeared Progressive Robot
Progressive Robot hmailserver
Vendors & Products Progressive Robot
Progressive Robot hmailserver

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

Type Values Removed Values Added
Description Inefficient algorithmic complexity in the webmail's message view of the REST API in Progressive Robot hMailServer 6.3.2 through 6.3.5 allows a remote unauthenticated attacker to make the webmail, the administration console and the REST API unavailable by sending a message. The route that renders a received message's HTML replaced each reference to an embedded image in place, with work that grew with the square of the number of references, and wrote the image out for every reference while counting it against its size limit only once. A message whose HTML refers to one small embedded image a very large number of times, opened in the webmail by its recipient, therefore keeps one of the listener's four worker threads busy for minutes and makes it build a document of gigabytes, so that a few such messages leave the HTTP listener unable to answer anybody.
Title Inefficient Algorithmic Complexity in hMailServer
Weaknesses CWE-407
References
Metrics cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H'}


Subscriptions

Progressive Robot Hmailserver
cve-icon MITRE

Status: PUBLISHED

Assigner: GitLab

Published:

Updated: 2026-10-08T14:14:10.184Z

Reserved: 2026-10-08T10:52:20.637Z

Link: CVE-2026-107583

cve-icon Vulnrichment

Updated: 2026-10-08T14:14:05.892Z

cve-icon NVD

Status : Received

Published: 2026-10-08T12:17:16.633

Modified: 2026-10-08T15:17:44.647

Link: CVE-2026-107583

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-08T13:45:05Z

Weaknesses