CWE - CWE-1254: Incorrect Comparison Logic Granularity (4.15)

Weakness ID: 1254

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's comparison logic is performed over a series of steps rather than across the entire string in one operation. If there is a comparison logic failure on one of these steps, the operation may be vulnerable to a timing attack that can result in the interception of the process for nefarious purposes.

Extended Description

Comparison logic is used to compare a variety of objects including passwords, Message Authentication Codes (MACs), and responses to verification challenges. When comparison logic is implemented at a finer granularity (e.g., byte-by-byte comparison) and breaks in the case of a comparison failure, an attacker can exploit this implementation to identify when exactly the failure occurred. With multiple attempts, the attacker may be able to guesses the correct password/response to challenge and elevate their privileges.

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 Authorization	Technical Impact: Bypass Protection Mechanism

Potential Mitigations

Phase: Implementation

The hardware designer should ensure that comparison logic is implemented so as to compare in one operation instead in smaller chunks.

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	Pillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things.	697	Incorrect Comparison
ChildOf	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.	208	Observable Timing Discrepancy
PeerOf	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.	1261	Improper Handling of Single Event Upsets

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.	1199	General Circuit and Logic Design Concerns

Modes Of Introduction

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: Not Technology-Specific (Undetermined Prevalence)

Demonstrative Examples

Example 1

Consider an example hardware module that checks a user-provided password to grant access to a user. The user-provided password is compared against a golden value in a byte-by-byte manner.

(bad code)

Example Language: Verilog

always_comb @ (posedge clk)

begin

assign check_pass[3:0] = 4'b0;
for (i = 0; i < 4; i++) begin

if (entered_pass[(i*8 - 1) : i] eq golden_pass([i*8 - 1) : i])

assign check_pass[i] = 1;
continue;

else

assign check_pass[i] = 0;
break;

end

assign grant_access = (check_pass == 4'b1111) ? 1'b1: 1'b0;

end

Since the code breaks on an incorrect entry of password, an attacker can guess the correct password for that byte-check iteration with few repeat attempts.

To fix this weakness, either the comparison of the entire string should be done all at once, or the attacker is not given an indication whether pass or fail happened by allowing the comparison to run through all bits before the grant_access signal is set.

(good code)

always_comb @ (posedge clk)
begin

assign check_pass[3:0] = 4'b0;
for (i = 0; i < 4; i++) begin

if (entered_pass[(i*8 - 1) : i] eq golden_pass([i*8 -1) : i])

assign check_pass[i] = 1;
continue;

else

assign check_pass[i] = 0;
continue;

end

assign grant_access = (check_pass == 4'b1111) ? 1'b1: 1'b0;

end

Observed Examples

Reference	Description
CVE-2019-10482	Smartphone OS uses comparison functions that are not in constant time, allowing side channels
CVE-2019-10071	Java-oriented framework compares HMAC signatures using String.equals() instead of a constant-time algorithm, causing timing discrepancies
CVE-2014-0984	Password-checking function in router terminates validation of a password entry when it encounters the first incorrect character, which allows remote attackers to obtain passwords via a brute-force attack that relies on timing differences in responses to incorrect password guesses, aka a timing side-channel attack.

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	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1417	Comprehensive Categorization: Sensitive Information Exposure

Vulnerability Mapping Notes

Usage: ALLOWED

(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.

Related Attack Patterns

CAPEC-ID	Attack Pattern Name
CAPEC-26	Leveraging Race Conditions

References

[REF-1079] Joe Fitzpatrick. "SCA4n00bz - Timing-based Sidechannel Attacks for Hardware N00bz workshop". <https://github.com/securelyfitz/SCA4n00bz>.

Content History

Submissions
Submission Date	Submitter	Organization
2020-02-12 (CWE 4.1, 2020-02-24)	Arun Kanuparthi, Hareesh Khattri, Parbati Kumar Manna, Narasimha Kumar V Mangipudi	Intel Corporation
2020-02-12 (CWE 4.1, 2020-02-24)
Modifications
Modification Date	Modifier	Organization
2020-08-20	CWE Content Team	MITRE
2020-08-20	updated Relationships
2021-07-20	CWE Content Team	MITRE
2021-07-20	updated Related_Attack_Patterns
2022-10-13	CWE Content Team	MITRE
2022-10-13	updated Demonstrative_Examples
2023-04-27	CWE Content Team	MITRE
2023-04-27	updated Observed_Examples, Relationships
2023-06-29	CWE Content Team	MITRE
2023-06-29	updated Mapping_Notes
2023-10-26	CWE Content Team	MITRE
2023-10-26	updated Demonstrative_Examples, Observed_Examples


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Common Weakness Enumeration

CWE-1254: Incorrect Comparison Logic Granularity

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