Skip to content
Fencer Intel
medium 6.5

CVE-2026-107582 json

Inefficient Algorithmic Complexity in hMailServer

published last mo. modified last mo. also EUVD-2026-94864

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 17%
public exploits
0
none known

Summary

Inefficient algorithmic complexity in the REST API (6.3.3 through 6.3.5) and the IMAP PREVIEW response (6.2.22 through 6.3.5) of Progressive Robot hMailServer allows a remote unauthenticated attacker to make the webmail, the administration console and the REST API unavailable by sending a message. To show a snippet of each message in a folder's message list, the server decoded the character entity references of a message that has an HTML part and no text part with a string replacement whose work grew with the square of their number. A received HTML-only message holding a very large number of entity references therefore keeps one of the listener's four worker threads busy for minutes or longer each time the recipient's webmail lists the folder, without the message being opened, so that a few such listings leave the HTTP listener unable to answer anybody. The IMAP PREVIEW response read such text the same way, holding an IMAP thread for each client that asks for the preview of such a message. The flaw is in the server's shared string class, whose replace and remove both ran in quadratic time.

Patch / fix

  • Progressive Robot Ltd hMailServer 6.3.6

Is CVE-2026-107582 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
last mo.

Exploit prediction

0.26% chance of exploitation in the next 30 days, higher than 17% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Affected products

  • Progressive Robot Ltd hMailServer

Classification

Weakness
  • CWE-407 Inefficient Algorithmic Complexity

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.