CVE-2026-114473 Progressive Robot Ltd CVE debrief

Who should care

Defenders managing hMailServer installations, especially those with SRS enabled, should assess exposure and prioritize patching to prevent unauthorized mail relaying. This includes verifying configurations, applying patches, and monitoring for suspicious activity. Additionally, security teams and vulnerability management teams should be aware of the potential impacts on mail server reputation and deliverability, and take steps to mitigate these risks.

Why it matters

CVE-2026-114473 allows remote attackers to relay mail through hMailServer 6.2.1-6.3.6 with SRS enabled, requiring defenders to verify configurations and apply patches.

• Potential unauthorized mail relaying through the server.
• Risk of spam or phishing campaigns using the vulnerable server.
• Need for verification of hMailServer configurations and patching.
• Possible impact on mail server reputation and deliverability.

Technical summary

The vulnerability is in the Sender Rewriting Scheme (SRS) of Progressive Robot hMailServer 6.2.1 through 6.3.6. SRS rewriting allows a remote attacker to relay mail through the server to outside addresses without proper authorization. This occurs because the server incorrectly handles mail forwarding with SRS enabled, allowing anyone with a valid SRS address to relay mail for 21 days. The issue arises from the server's failure to apply relay rules and SMTP authentication requirements when delivering mail to an encoded SRS address, effectively bypassing security measures meant to prevent unauthorized mail relaying.

Defensive priority

Defenders should prioritize verifying hMailServer configurations, especially SRS settings, and apply patches to prevent unauthorized mail relaying.

Recommended defensive actions

• Verify hMailServer configurations, especially SRS settings.
• Apply patches to prevent unauthorized mail relaying.
• Monitor mail server logs for suspicious activity.
• Restrict SRS address usage to trusted recipients.
• 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 references to vendor releases. However, the corpus does not establish specific exploitation instances or remediation beyond patching.

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.