CVE-2026-107586 Progressive Robot Ltd CVE debrief

Who should care

hMailServer administrators, security teams, and IT professionals responsible for managing and securing email servers should assess exposure and apply patches or mitigations to prevent potential session termination attacks.

Why it matters

CVE-2026-107586 is a medium-severity vulnerability in hMailServer that allows remote authenticated users to end other users' sessions. hMailServer administrators and security teams should assess exposure, apply patches, and monitor for suspicious activity to prevent potential session termination attacks.

• Remote authenticated users can terminate other users' sessions, potentially disrupting email access and administration.
• hMailServer administrators need to assess exposure and apply patches to prevent exploitation.
• The vulnerability requires verification of affected versions and patch application to mitigate potential impact.
• Defenders should monitor for suspicious session activity and implement additional logging and monitoring measures.

Technical summary

The REST API in Progressive Robot hMailServer 6.2.28 through 6.3.5 has an uncontrolled eviction in the browser session table, allowing a remote authenticated user to end other users' sessions. The table, shared by every account, the server administrator, and support sessions, drops its least recently used session whenever it is full, without limiting the number of sessions one account can hold. This vulnerability requires verification of affected versions and patch application to mitigate potential impact. Defenders should monitor for suspicious session activity and implement additional logging and monitoring measures.

Defensive priority

Medium priority for hMailServer administrators and security teams to assess exposure and apply patches.

Recommended defensive actions

• Assess exposure by checking if hMailServer versions 6.2.28 through 6.3.5 are in use.
• Apply patches or upgrade to version 6.3.6 or later.
• Monitor for suspicious session activity and implement additional logging and monitoring measures.
• Review and update incident response plans to address potential session termination attacks.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.

Evidence notes

The CVE record and source item provide details on the vulnerability, affected versions, and potential impact. However, limited information is available on exploitation, victims, or business impact. Defenders should verify the affected versions, assess exposure, and apply patches to mitigate potential impact. Additional logging and monitoring measures should be implemented to detect suspicious session activity.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.