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A community-developed list of SW & HW weaknesses that can become vulnerabilities
CWE-208: Observable Timing Discrepancy
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Description Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not.
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Extended Description
In security-relevant contexts, even small variations in timing can be exploited by attackers to indirectly infer certain details about the product's internal operations. For example, in some cryptographic algorithms, attackers can use timing differences to infer certain properties about a private key, making the key easier to guess. Timing discrepancies effectively form a timing side channel.
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Common Consequences 👁 Section Help
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.
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Relationships
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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.
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Relevant to the view "Research Concepts" (View-1000)
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Relevant to the view "Software Development" (View-699)
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Relevant to the view "Architectural Concepts" (View-1008)
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Modes Of Introduction 👁 Section Help
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.
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Applicable Platforms 👁 Section Help
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.
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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;
endfor (i = 0; i < 4; i++) begin
if (entered_pass[(i*8 - 1) : i] eq golden_pass([i*8 - 1) : i])
assign grant_access = (check_pass == 4'b1111) ? 1'b1: 1'b0;
assign check_pass[i] = 1;
elsecontinue;
assign check_pass[i] = 0;
endbreak; 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)
Example Language: Verilog
always_comb @ (posedge clk)
begin
assign check_pass[3:0] = 4'b0;
endfor (i = 0; i < 4; i++) begin
if (entered_pass[(i*8 - 1) : i] eq golden_pass([i*8 -1) : i])
assign grant_access = (check_pass == 4'b1111) ? 1'b1: 1'b0;
assign check_pass[i] = 1;
elsecontinue;
assign check_pass[i] = 0;
endcontinue; Example 2 In this example, the attacker observes how long an authentication takes when the user types in the correct password. When the attacker tries their own values, they can first try strings of various length. When they find a string of the right length, the computation will take a bit longer, because the for loop will run at least once. Additionally, with this code, the attacker can possibly learn one character of the password at a time, because when they guess the first character right, the computation will take longer than a wrong guesses. Such an attack can break even the most sophisticated password with a few hundred guesses. (bad code)
Example Language: Python
def validate_password(actual_pw, typed_pw):
if len(actual_pw) <> len(typed_pw):
return 0
for i in len(actual_pw): if actual_pw[i] <> typed_pw[i]:
return 0
return 1 Note that in this example, the actual password must be handled in constant time as far as the attacker is concerned, even if the actual password is of an unusual length. This is one reason why it is good to use an algorithm that, among other things, stores a seeded cryptographic one-way hash of the password, then compare the hashes, which will always be of the same length. 👁 +
Selected Observed Examples Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.
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Weakness Ordinalities
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Functional Areas
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Memberships
👁 Section Help
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.
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Vulnerability Mapping Notes
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Notes Relationship
Often primary in cryptographic applications and algorithms.
Maintenance
CWE 4.16 removed a demonstrative example for a hardware module because it was inaccurate and unable to be adapted. The CWE team is developing an alternative.
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Taxonomy Mappings
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Related Attack Patterns 👁 +
Content History
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