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CVE-2018-25396 Heatmiser CVE debrief

CVE-2018-25396 documents a credential disclosure vulnerability in Heatmiser Wifi Thermostat firmware version 1.7. The device exposes administrative credentials in plaintext within the HTML source of the networkSetup.htm page, allowing unauthenticated remote attackers to retrieve username and password values by requesting this endpoint. This represents a critical information exposure weakness (CWE-256: Unprotected Storage of Credentials) where sensitive authentication data is embedded directly in client-accessible markup rather than being server-side protected or encrypted at rest. The vulnerability carries a HIGH severity CVSS 4.0 score of 8.7, reflecting network attack vector with low complexity, no privileges required, and high impact to confidentiality of the thermostat's administrative interface. The CVE was published to NVD on 2026-05-29 with vulnerability status 'Received'. No known exploitation in ransomware campaigns has been documented, and the vulnerability is not listed in CISA KEV.

Vendor
Heatmiser
Product
Heatmiser Wifi Thermostat
CVSS
HIGH 8.7
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-29
Original CVE updated
2026-05-29
Advisory published
2026-05-29
Advisory updated
2026-05-29

Who should care

Organizations deploying Heatmiser Wifi Thermostats in commercial or residential environments; facilities management teams responsible for building automation security; IoT security assessors; network administrators managing HVAC control systems; and security teams monitoring for credential exposure in embedded devices.

Technical summary

The Heatmiser Wifi Thermostat firmware 1.7 embeds administrative credentials in plaintext within the HTML response of the networkSetup.htm page. An unauthenticated HTTP GET request to this endpoint returns a form containing visible username and password fields populated with current administrative credentials. This design flaw enables credential harvesting without authentication, granting attackers full administrative control over the device. The vulnerability is remotely exploitable with no user interaction required.

Defensive priority

HIGH

Recommended defensive actions

  • Audit network segmentation to restrict access to Heatmiser thermostat administrative interfaces from untrusted networks
  • Review device firmware and apply vendor patches if available; consider firmware upgrade paths given 2018 vulnerability date
  • Implement network monitoring for unauthorized requests to networkSetup.htm or similar administrative endpoints
  • If vendor patches are unavailable, consider isolating affected thermostats on dedicated management VLANs with strict access controls
  • Document and rotate any credentials that may have been exposed through this vulnerability
  • Evaluate replacement of end-of-life IoT devices that cannot receive security updates

Evidence notes

Primary evidence sources include NVD CVE record with CVSS 4.0 vector, VulnCheck advisory, and Exploit-DB reference. CPE criteria were not available in source data. CWE-256 (Unprotected Storage of Credentials) is identified as the primary weakness. Vendor identification is marked low confidence with 'Unknown Vendor' in source data, though product attribution to Heatmiser is explicit in references.

Official resources

The vulnerability was disclosed via VulnCheck advisory and published to Exploit-DB. The disclosure identifies specific firmware version 1.7 as affected and documents the networkSetup.htm endpoint as the exposure point. Vendor attribution is