Watchfire Controllers Ship Hard-Coded RSA Keys

Watchfire BC-series battery controllers embed hard-coded RSA private keys in firmware, letting attackers push malicious firmware updates and take full control.

CISA has published an advisory for Watchfire Controller Software affecting the BC550, BC750, BC760, and BC760DC product lines. The vulnerability, tracked as CVE-2026-5846, stems from self-signed, hard-coded RSA private keys and corresponding X.509 certificates used to authenticate and encrypt HTTPS/TLS connections to the controller's built-in web management interface. These keys are stored in plaintext within application patch binaries distributed through Watchfire's Remote Support filestore, meaning anyone with access to the firmware files could extract the keys and use them to deliver malicious firmware updates, ultimately gaining full control of affected controllers.

Watchfire has already applied a security patch to all controllers under its management and has issued updated firmware versions that disable use of the existing compromised certificates. Organizations still running unpatched versions are urged to upgrade to the specified fixed releases. The affected products are deployed across critical infrastructure sectors including commercial facilities, critical manufacturing, healthcare and public health, and financial services, with installations in the United States, Dominican Republic, Canada, Peru, and El Salvador.

CISA notes no known public exploitation of this vulnerability has been reported, and rates the attack complexity as high. Standard ICS defense-in-depth guidance applies: minimizing internet exposure of control system devices, isolating ICS networks behind firewalls, and using secure remote access methods such as VPNs where necessary.

Source reporting: https://www.cisa.gov/news-events/ics-advisories/icsa-26-211-09