CVE-2026-107585: Allocation of Resources Without Limits or Throttling in hMailServer

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-08 · updated 2026-10-08
Weakness: CWE-770

Description

Uncontrolled eviction in the pending sign-in tables of the REST API in Progressive Robot hMailServer 6.3.4 and 6.3.5 allows a remote unauthenticated attacker to make other users' OpenID Connect, SAML and passkey sign-ins fail. The routes that start a single sign-on and hand out a passkey sign-in challenge are reached without authentication and stored pending state in bounded tables that dropped their oldest entry when full, whoever had started it. An attacker who starts sign-ins a few times a second (about a hundred a second for passkeys) pushes every other user's pending sign-in out of the table before that user's browser returns, denying single sign-on and passkey sign-in for as long as the requests continue.

Affected products

Progressive Robot Ltd hMailServer: from 6.3.4 before 6.3.6 — fixed in 6.3.6

How to fix

Upgrade to a fixed version: Progressive Robot Ltd hMailServer 6.3.6. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-107585 or the next vulnerability affects your stack