CWE-1244: Internal Asset Exposed to Unsafe Debug Access Level or State
Weakness ID: 1244
Vulnerability Mapping:
ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities Abstraction: BaseBase - 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.
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Description
The product uses physical debug or test interfaces with support for multiple access levels, but it assigns the wrong debug access level to an internal asset, providing unintended access to the asset from untrusted debug agents.
Extended Description
Debug authorization can have multiple levels of access, defined such that different system internal assets are accessible based on the current authorized debug level. Other than debugger authentication (e.g., using passwords or challenges), the authorization can also be based on the system state or boot stage. For example, full system debug access might only be allowed early in boot after a system reset to ensure that previous session data is not accessible to the authenticated debugger.
If this protection mechanism does not ensure that internal assets have the correct debug access level during each boot stage or change in system state, an attacker could obtain sensitive information from the internal asset using a debugger.
Relationships
This table 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.
This table 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 "Hardware Design" (CWE-1194)
Nature
Type
ID
Name
MemberOf
Category - a CWE entry that contains a set of other entries that share a common characteristic.
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
Implementation
Applicable Platforms
This listing shows 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.
Languages
Class: Not Language-Specific (Undetermined Prevalence)
Operating Systems
Class: Not OS-Specific (Undetermined Prevalence)
Architectures
Class: Not Architecture-Specific (Undetermined Prevalence)
Technologies
Class: System on Chip (Undetermined Prevalence)
Common Consequences
This table 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.
Scope
Impact
Likelihood
Confidentiality
Technical Impact: Read Memory
Integrity
Technical Impact: Modify Memory
Authorization Access Control
Technical Impact: Gain Privileges or Assume Identity; Bypass Protection Mechanism
Demonstrative Examples
Example 1
The JTAG interface is used to perform debugging and provide CPU core access for developers. JTAG-access protection is implemented as part of the JTAG_SHIELD bit in the hw_digctl_ctrl register. This register has no default value at power up and is set only after the system boots from ROM and control is transferred to the user software.
(bad code)
Example Language: Other
1 bit
0x0 = JTAG debugger is enabled (default)
JTAG_SHIELD
0x1 = JTAG debugger is disabled
This means that since the end user has access to JTAG at system reset and during ROM code execution before control is transferred to user software, a JTAG user can modify the boot flow and subsequently disclose all CPU information, including data-encryption keys.
(informative)
The default value of this register bit should be set to 1 to prevent the JTAG from being enabled at system reset.
Example 2
The example code below is taken from the CVA6 processor core of the HACK@DAC'21 buggy OpenPiton SoC. Debug access allows users to access internal hardware registers that are otherwise not exposed for user access or restricted access through access control protocols. Hence, requests to enter debug mode are checked and authorized only if the processor has sufficient privileges. In addition, debug accesses are also locked behind password checkers. Thus, the processor enters debug mode only when the privilege level requirement is met, and the correct debug password is provided.
The following code [REF-1377] illustrates an instance of a vulnerable implementation of debug mode. The core correctly checks if the debug requests have sufficient privileges and enables the debug_mode_d and debug_mode_q signals. It also correctly checks for debug password and enables umode_i signal.
(bad code)
Example Language: Verilog
module csr_regfile #(
...
// check that we actually want to enter debug depending on the privilege level we are currently in
unique case (priv_lvl_o)
However, it grants debug access and changes the privilege level, priv_lvl_o, even when one of the two checks is satisfied and the other is not. Because of this, debug access can be granted by simply requesting with sufficient privileges (i.e., debug_mode_q is enabled) and failing the password check (i.e., umode_i is disabled). This allows an attacker to bypass the debug password checking and gain debug access to the core, compromising the security of the processor.
A fix to this issue is to only change the privilege level of the processor when both checks are satisfied, i.e., the request has enough privileges (i.e., debug_mode_q is enabled) and the password checking is successful (i.e., umode_i is enabled) [REF-1378].
(good code)
Example Language: Verilog
module csr_regfile #(
...
// check that we actually want to enter debug depending on the privilege level we are currently in
unique case (priv_lvl_o)
After ROM code execution, JTAG access is disabled. But before the ROM code is executed, JTAG access is possible, allowing a user full system access. This allows a user to modify the boot flow and successfully bypass the secure-boot process.
Potential Mitigations
Phases: Architecture and Design; Implementation
For security-sensitive assets accessible over debug/test interfaces, only allow trusted agents.
Effectiveness: High
Phase: Architecture and Design
Apply blinding [REF-1219] or masking techniques in strategic areas.
Effectiveness: Limited
Phase: Implementation
Add shielding or tamper-resistant protections to the device, which increases the difficulty and cost for accessing debug/test interfaces.
Effectiveness: Limited
Weakness Ordinalities
Ordinality
Description
Primary
(where the weakness exists independent of other weaknesses)
Detection Methods
Manual Analysis
Check 2 devices for their passcode to authenticate access to JTAG/debugging ports. If the passcodes are missing or the same, update the design to fix and retest. Check communications over JTAG/debugging ports for encryption. If the communications are not encrypted, fix the design and retest.
Effectiveness: Moderate
Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
Nature
Type
ID
Name
MemberOf
View - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).
(this CWE ID could be used to map to real-world vulnerabilities)
Reason: Acceptable-Use
Rationale:
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comments:
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.
Notes
Relationship
CWE-1191 and CWE-1244 both involve physical debug access, but the weaknesses are different. CWE-1191 is effectively about missing authorization for a debug interface, i.e. JTAG. CWE-1244 is about providing internal assets with the wrong debug access level, exposing the asset to untrusted debug agents.
Description
This table 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.
