Improper Protection for Outbound Error Messages and Alert Signals

Draft Base
Structure: Simple
Description

Untrusted agents can disable alerts about signal conditions exceeding limits or the response mechanism that handles such alerts.

Extended Description

Hardware sensors are used to detect whether a device is operating within design limits. The threshold values for these limits are set by hardware fuses or trusted software such as a BIOS. Modification of these limits may be protected by hardware mechanisms. When device sensors detect out of bound conditions, alert signals may be generated for remedial action, which may take the form of device shutdown or throttling. Warning signals that are not properly secured may be disabled or used to generate spurious alerts, causing degraded performance or denial-of-service (DoS). These alerts may be masked by untrusted software. Examples of these alerts involve thermal and power sensor alerts.

Common Consequences 1
Scope: Availability

Impact: DoS: InstabilityDoS: Crash, Exit, or RestartReduce ReliabilityUnexpected State

Potential Mitigations 1
Phase: Architecture and Design
Alert signals generated by critical events should be protected from access by untrusted agents. Only hardware or trusted firmware modules should be able to alter the alert configuration.
Demonstrative Examples 1
Consider a platform design where a Digital-Thermal Sensor (DTS) is used to monitor temperature and compare that output against a threshold value. If the temperature output equals or exceeds the threshold value, the DTS unit sends an alert signal to the processor. The processor, upon getting the alert, input triggers system shutdown. The alert signal is handled as a General-Purpose-I/O (GPIO) pin in input mode.

Code Example:

Bad
Other

The processor-GPIO controller exposes software-programmable controls that allow untrusted software to reprogram the state of the GPIO pin.

Reprogramming the state of the GPIO pin allows malicious software to trigger spurious alerts or to set the alert pin to a zero value so that thermal sensor alerts are not received by the processor.

Code Example:

Good
Other

The GPIO alert-signal pin is blocked from untrusted software access and is controlled only by trusted software, such as the System BIOS.

Applicable Platforms
Languages:
Not Language-Specific : Undetermined
Technologies:
System on Chip : UndeterminedMicrocontroller Hardware : UndeterminedMemory Hardware : UndeterminedPower Management Hardware : UndeterminedProcessor Hardware : UndeterminedTest/Debug Hardware : UndeterminedSensor Hardware : Undetermined
Modes of Introduction
Architecture and Design
Implementation
Related Weaknesses