CVE-2026-107579: high-severity vulnerability in Progressive Robot Ltd hMailServer
Inefficient Algorithmic Complexity in hMailServer
Published
21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 7.5epss 0.3%
exploitation probability
0.3%top 74% of all CVEs
observed exploitation
nono source reports it
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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Affected products
Progressive Robot Ltd · hMailServerRelated CVEs — Progressive Robot Ltd hMailServer
In the same product, most dangerous first.
CVE-2026-100741CRITICALImproper Neutralization of Directives in Dynamically Evaluated Code ('Eval Injection') in hMailServerEPSS 1.7%CVE-2026-107585MEDIUMAllocation of Resources Without Limits or Throttling in hMailServerEPSS 0.4%CVE-2026-107576HIGHInefficient Algorithmic Complexity in hMailServerEPSS 0.4%CVE-2026-107577HIGHLoop with Unreachable Exit Condition ('Infinite Loop') in hMailServerEPSS 0.4%CVE-2026-107574HIGHInefficient Algorithmic Complexity in hMailServerEPSS 0.4%CVE-2026-107575MEDIUMInefficient Algorithmic Complexity in hMailServerEPSS 0.4%