Key Takeaways
- Physically disconnecting an infected device from all power sources for at least one minute performs a “cold start” that clears volatile memory and disrupts malware’s boot‑time persistence.
- This mitigates damage by removing the malware that resides only in RAM, preventing it from re‑loading after a normal reboot.
- Network administrators should replace legacy authentication methods with TACACS+ transported over TLS 1.3 to strengthen access control for routers, switches, and firewalls.
- Because TACACS+ uses a dedicated TCP port, existing firewall rules must be updated to allow the new traffic, and Cisco devices require ISE 3.4 (or later) to support the protocol.
- When deploying TACACS+ in heterogeneous environments, consult each vendor’s documentation to ensure interoperability and avoid authentication failures.
Introduction to the Threat and Mitigation Advice
Recent guidance from the Cybersecurity and Infrastructure Security Agency (CISA) and Cisco highlights a specific class of malware that survives normal reboots by embedding itself in a device’s volatile memory and establishing boot‑time persistence. The advisory stresses that the most reliable way to eradicate this threat is to perform a physical power‑cycle that removes all sources of electricity—including redundant power supplies and UPS units—for a minimum of sixty seconds. This “cold start” forces the hardware to lose its RAM contents, thereby eliminating the malicious code that resides only there. By following this step, administrators can break the malware’s persistence chain and prevent it from re‑infecting the device upon restoration of power.
The Concept of a Cold Start and Its Effect on Volatile Memory
Volatile memory, such as DRAM, retains data only while powered; once the supply is cut, the stored bits decay rapidly, typically within milliseconds to a few seconds depending on temperature and refresh rates. Malware that relies on RAM‑resident components—often used to hide malicious code, hold encryption keys, or maintain a covert channel—cannot survive a complete loss of power. A cold start therefore acts as a hardware‑level sanitizer: it flushes the memory space where the malware lurks, erasing any payload, configuration artifacts, or persistence mechanisms that would otherwise be re‑loaded during a soft reboot. This approach is especially effective against file‑less or memory‑only threats that leave little trace on persistent storage.
Why Disconnecting Power for at Least One Minute is Critical
While a brief power loss may clear most RAM, certain hardware designs retain residual charge in capacitors or employ fast‑wake circuits that can preserve a faint imprint of data for a short interval. Security researchers have demonstrated that, under optimal conditions, some bits can linger for up to several tens of seconds. By mandating a full sixty‑second disconnection—covering both primary and redundant power supplies—the guidance provides a safety margin that ensures even the most stubborn residual charge dissipates completely. This interval also allows time for any auxiliary power sources (e.g., backup batteries) to drain, guaranteeing a true “cold” state before the device is re‑energized.
Modernizing Administrative Controls with TACACS+ over TLS 1.3
Beyond removing existing infections, the advisory urges organizations to harden the authentication pathways used to manage network infrastructure. Enderle recommends transitioning from legacy protocols such as RADIUS or plain‑text TACACS+ to TACACS+ encapsulated within Transport Layer Security version 1.3 (TLS 1.3). TLS 1.3 offers forward secrecy, reduced handshake latency, and strong cipher suites, thereby protecting credential exchanges from eavesdropping and man‑in‑the‑middle attacks. By coupling TACACS+’s granular command‑level authorization with TLS 1.3’s encryption, administrators gain both robust access control and confidential communication for routers, switches, and firewalls.
Technical Requirements: TCP Port Usage and Firewall Rule Adjustments
TACACS+ traditionally operates over a single TCP port—most commonly port 49. When the protocol is wrapped in TLS, the same port continues to be used, but the traffic now appears as encrypted TLS streams. Consequently, any existing firewall policies that either block or implicitly allow TACACS+ traffic must be reviewed and updated to explicitly permit TLS‑wrapped packets on port 49. Administrators should also consider logging and inspecting the TLS handshake (where permissible) to detect anomalous connection attempts. Failure to adjust these rules could result in locked‑out management sessions or, conversely, inadvertent exposure of the management plane to unauthorized entities.
Cisco Identity Services Engine Patch Necessities
For Cisco‑centric environments, the Identity Services Engine (ISE) serves as the central policy engine that authenticates and authorizes devices using TACACS+. To support TACACS+ over TLS 1.3, Cisco mandates ISE version 3.4 or later, which includes the necessary TLS library updates and protocol handlers. Older ISE releases lack support for TLS 1.3’s cryptographic suites and may reject the encrypted TACACS+ packets, leading to authentication failures. Organizations should therefore schedule an upgrade to ISE 3.4 (or a newer patch) before attempting to enable the secure TACACS+ mode, ensuring that the policy engine can correctly decrypt and process incoming authentication requests.
Ensuring Interoperability Across Multi‑Vendor Environments
Many networks incorporate equipment from various manufacturers, each with its own implementation of TACACS+ and TLS support. Before migrating to TACACS+ over TLS 1.3, administrators should consult the documentation of all relevant vendors—such as Juniper, Arista, Palo Alto Networks, and others—to verify that their devices can both send and receive TACACS+ packets encapsulated in TLS 1.3. Some platforms may require firmware upgrades, separate licensing, or specific configuration toggles (e.g., enabling “TACACS+ over TLS” mode). Conducting a lab‑based proof‑of‑concept that includes a representative sample of each device type helps uncover incompatibilities early, preventing authentication outages during the production rollout.
Synthesizing the Recommendations into a Practical Action Plan
To operationalize the guidance, organizations should first execute a cold‑start remediation on any suspected infected device: disconnect all power sources, wait at least sixty seconds, then reconnect and verify system integrity. Next, prioritize the upgrade of authentication infrastructure: update firewall rules to allow TLS‑wrapped TACACS+ on port 49, upgrade Cisco ISE to version 3.4 or newer, and verify that non‑Cisco gear supports the new mode. Where gaps exist, plan staged firmware updates or vendor‑specific patches. Finally, maintain continuous monitoring of authentication logs and network traffic to detect any attempts to bypass the new controls, ensuring that the combination of hardware‑level sanitization and strengthened, encrypted access controls provides a layered defense against both current and future threats.