CWE-1314: Missing Write Protection for Parametric Data Values
Weakness ID: 1314
Abstraction: Base Structure: Simple
Status: Draft
Presentation Filter:
Description
The device does not write-protect the parametric data values for sensors that scale the sensor value, allowing untrusted software to manipulate the apparent result and potentially damage hardware or cause operational failure.
Extended Description
Various sensors are used by hardware to detect any devices operating outside of the design limits. The threshold limit values are set by hardware fuses or trusted software such as the BIOS. These limits may be related to thermal, power, voltage, current, and frequency. Hardware mechanisms may be used to protect against alteration of the threshold limit values by untrusted software.
The limit values are generally programmed in standard units for the type of value being read. However, the hardware-sensor blocks may report the settings in different units depending upon sensor design and operation. The raw sensor output value is converted to the desired units using a scale conversion based on the parametric data programmed into the sensor. The final converted value is then compared with the previously programmed limits.
While the limit values are usually protected, the sensor parametric data values may not be. By changing the parametric data, safe operational limits may be bypassed.
Relationships
The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
Relevant to the view "Research Concepts" (CWE-1000)
Nature
Type
ID
Name
ChildOf
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
Base - a weakness
that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
Phase
Note
Architecture and Design
The lack of a requirement to protect parametric values may contribute to this weakness.
Implementation
The lack of parametric value protection may be a cause of this weakness.
Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.
The table below specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
Sensor value manipulation, particularly thermal or power, may allow physical damage to occur or disabling of the device by a false fault shutdown causing a Denial-Of-Service.
High
Demonstrative Examples
Example 1
Malicious software executes instructions to increase power consumption to the highest possible level while causing the clock frequency to increase to its maximum value.
Such a program executing for an extended period of time would likely overheat the device, possibly resulting in permanent damage to the device.
A ring, oscillator-based temperature sensor will generally report the sensed value as
oscillator frequency rather than degrees centigrade. The temperature sensor will have
calibration values that are used to convert the detected frequency into the corresponding temperature in degrees centigrade.
Consider a SoC design where the critical maximum temperature limit is set in fuse values to 100C and
is not modifiable by software. If the scaled thermal sensor output equals or exceeds this limit, the system is commanded to shut itself down.
The thermal sensor calibration values are programmable through registers that are exposed to system software.
These registers allow software to affect the converted temperature output such that the output will never exceed the maximum temperature limit.
(bad code)
Example Language: Other
The sensor frequency value is scaled by applying the function:
Sensed Temp = a + b * Sensor Freq
where a and b are the programmable calibration data coefficients. Software sets a and b to zero ensuring the sensed
temperature is always zero.
This weakness may be addressed by preventing access to a and b.
(good code)
Example Language: Other
The sensor frequency value is scaled by applying the function:
Sensed Temp = a + b * Sensor Freq
where a and b are the programmable calibration data coefficients. Untrusted software is prevented from changing the values of either a or b,
preventing this method of manipulating the temperature.
Kernel can inject faults in computations during the execution of TrustZone leading to information disclosure in Snapdragon Auto, Snapdragon Compute, Snapdragon Connectivity, Snapdragon Consumer Electronics Connectivity, Snapdragon Consumer IOT, Snapdragon Industrial IOT, Snapdragon IoT, Snapdragon Mobile, Snapdragon Voice and Music, Snapdragon Wearables, Snapdragon Wired Infrastructure and Networking.
Potential Mitigations
Phase: Architecture and Design
Access controls for sensor blocks should ensure that only trusted software is allowed to change threshold limits and sensor parametric data.
Description
