CWE-1255: Comparison Logic is Vulnerable to Power Side-Channel Attacks

Extended Description

The power consumed by a device may be instrumented and monitored in real time. If the algorithm for evaluating security tokens is not sufficiently robust, the power consumption may vary by token entry comparison against the reference value. Further, if retries are unlimited, the power difference between a "good" entry and a "bad" entry may be observed and used to determine whether each entry itself is correct thereby allowing unauthorized parties to calculate the reference value.

Code Examples & CVEs

Demonstrative Examples

Consider an example hardware module that checks a user-provided password (or PIN) to grant access to a user. The user-provided password is compared against a stored value byte-by-byte.

Since the algorithm uses a different number of 1's and 0's for password validation, a different amount of power is consumed for the good byte versus the bad byte comparison. Using this information, an attacker may be able to guess the correct password for that byte-by-byte iteration with several repeated attempts by stopping the password evaluation before it completes.

BadC

static nonvolatile password_tries = NUM_RETRIES;            do 	                 while (password_tries == 0) ; // Hang here if no more password tries              password_ok = 0;              for (i = 0; i < NUM_PW_DIGITS; i++) 	                     if (GetPasswordByte() == stored_password([i]) 	        		 password_ok |= 1; // Power consumption is different here 	                       else 	        		 password_ok |= 0; // than from here 	        	                   end              if (password_ok > 0) 	                     password_tries = NUM_RETRIES;                break_to_Ok_to_proceed 	                   password_tries--; 	               while (true)            // Password OK

Consider an example hardware module that checks a user-provided password (or PIN) to grant access to a user. The user-provided password is compared against a stored value byte-by-byte.

GoodC

static nonvolatile password_tries = NUM_RETRIES;            do 	                 while (password_tries == 0) ; // Hang here if no more password tries              password_tries--;  // Put retry code here to catch partial retries              password_ok = 0;              for (i = 0; i < NUM_PW_DIGITS; i++) 	                     if (GetPasswordByte() == stored_password([i]) 	        		 password_ok |= 0x10; // Power consumption here 	                       else 	        		 password_ok |= 0x01; // is now the same here 	        	                   end              if ((password_ok & 1) == 0) 	                     password_tries = NUM_RETRIES;                break_to_Ok_to_proceed 	      	               while (true)            // Password OK

This code demonstrates the transfer of a secret key using Serial-In/Serial-Out shift. It's easy to extract the secret using simple power analysis as each shift gives data on a single bit of the key.

This code demonstrates the transfer of a secret key using a Parallel-In/Parallel-Out shift. In a parallel shift, data confounded by multiple bits of the key, not just one.

BadVerilog

module siso(clk,rst,a,q); 	                   input a;               input clk,rst;               output q;               reg q;                              always@(posedge clk,posedge rst)               begin 	       		if(rst==1'b1) 		                   q<1'b0; 		 		else 		                   q<a; 		 	                     end 	                 endmodule

This code demonstrates the transfer of a secret key using Serial-In/Serial-Out shift. It's easy to extract the secret using simple power analysis as each shift gives data on a single bit of the key.

This code demonstrates the transfer of a secret key using a Parallel-In/Parallel-Out shift. In a parallel shift, data confounded by multiple bits of the key, not just one.

GoodVerilog

module pipo(clk,rst,a,q); 	                 input clk,rst;              input[3:0]a;              output[3:0]q;              reg[3:0]q;                            always@(posedge clk,posedge rst)              begin 	                     if (rst==1'b1) 	                         q<4'b0000; 	                       else 	                         q<a; 	        	                   end 	               endmodule

Observed CVE Examples (1)

CVE-2020-12788

CMAC verification vulnerable to timing and power attacks.

View Details

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-1255 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-1255, Comparison Logic is Vulnerable to Power Side-Channel Attacks, throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Address Comparison Logic is Vulnerable to Power Side-Channel Attacks during Architecture and Design

MITRE associates mitigation with Architecture and Design, Implementation, and Integration; recorded impacts include Modify Memory, Read Memory, Read Files or Directories, Modify Files or Directories, and Execute Unauthorized Code or Commands; the entry maps to CAPEC-189. Use these source-defined anchors to turn CWE-1255 into implementation, review, and verification checks for the affected component.

CWE-1255: Comparison Logic is Vulnerable to Power Side-Channel Attacks — MITRE CWE

Triage CWE-1255 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-1255, Comparison Logic is Vulnerable to Power Side-Channel Attacks, has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Apply precise root-cause mapping to CWE-1255

Apply MITRE's full root-cause mapping guidance when using CWE-1255, Comparison Logic is Vulnerable to Power Side-Channel Attacks. Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-1255 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-1255, Comparison Logic is Vulnerable to Power Side-Channel Attacks. Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE CWE

Frequently Asked Questions

What is CWE-1255: Comparison Logic is Vulnerable to Power Side-Channel Attacks?+

CWE-1255: Comparison Logic is Vulnerable to Power Side-Channel Attacks is a Common Weakness Enumeration (CWE) entry maintained by MITRE. A device's real time power consumption may be monitored during security token evaluation and the information gleaned may be used to determine the value of the reference token. The power consumed by a device may be instrumented and monitored in real time. If the algorithm for evaluating security tokens is not sufficiently robust, the power consumption may vary by token entry comparison against the reference value. Further, if retries are unlimited, the power difference between a "good" entry and a "bad" entry may be observed and used to determine whether each entry itself is correct thereby allowing unauthorized parties to calculate the reference value.

What are the security consequences of Comparison Logic is Vulnerable to Power Side-Channel Attacks?+

If exploited, CWE-1255 (Comparison Logic is Vulnerable to Power Side-Channel Attacks) it can compromise Confidentiality, Integrity, Availability, Access Control, Accountability and Authentication, leading to outcomes such as Modify Memory, Read Memory, Read Files or Directories, Modify Files or Directories, Execute Unauthorized Code or Commands and Gain Privileges or Assume Identity.

How do you prevent or mitigate Comparison Logic is Vulnerable to Power Side-Channel Attacks?+

Recommended mitigations for CWE-1255 include: The design phase must consider each check of a security token against a standard and the amount of power consumed during the check of a good token versus a bad token. The alternative is an all at once check where a retry counter is incremented PRIOR to the check. Another potential mitigation is to parallelize shifting of secret data (see example 2 below). Note that the wider the bus the more effective the result. An additional potential mitigation is to add random data to each crypto operation then subtract it out afterwards. This is highly effective but costly in performance, area, and power consumption. It also requires a random number generator.

Which programming languages are affected by Comparison Logic is Vulnerable to Power Side-Channel Attacks?+

CWE-1255 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What are real-world examples of Comparison Logic is Vulnerable to Power Side-Channel Attacks?+

MITRE documents real CVEs mapped to CWE-1255, including CVE-2020-12788. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-1255 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.

CWE-1255: Comparison Logic is Vulnerable to Power Side-Channel Attacks

Extended Description

Technical Details

Applicable To

Security Consequences

Scope

Impact

Mitigation Strategies

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Detection Methods

Code Examples & CVEs

Demonstrative Examples

Observed CVE Examples (1)

CWE Relationships

Parent Weaknesses

Source-backed guidance

Verify controls for CWE-1255 with SSDF evidence

Address Comparison Logic is Vulnerable to Power Side-Channel Attacks during Architecture and Design

Triage CWE-1255 against known exploitation evidence

Apply precise root-cause mapping to CWE-1255

Validate CWE-1255 with root-cause mapping checks

Frequently Asked Questions

Learn More