CWE

Common Weakness Enumeration

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ID

CWE-385: Covert Timing Channel

Weakness ID: 385
Abstraction: Base
Structure: Simple
View customized information:
+ Description
Covert timing channels convey information by modulating some aspect of system behavior over time, so that the program receiving the information can observe system behavior and infer protected information.
+ Extended Description

In some instances, knowing when data is transmitted between parties can provide a malicious user with privileged information. Also, externally monitoring the timing of operations can potentially reveal sensitive data. For example, a cryptographic operation can expose its internal state if the time it takes to perform the operation varies, based on the state.

Covert channels are frequently classified as either storage or timing channels. Some examples of covert timing channels are the system's paging rate, the time a certain transaction requires to execute, and the time it takes to gain access to a shared bus.

+ Relationships
Section HelpThis 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)
NatureTypeIDName
ChildOfClassClass - 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.514Covert Channel
CanFollowBaseBase - 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.208Observable Timing Discrepancy
Section HelpThis 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 "Software Development" (CWE-699)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.417Communication Channel Errors
+ Modes Of Introduction
Section HelpThe 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.
PhaseNote
Architecture and Design
Implementation
+ Applicable Platforms
Section HelpThis 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)

+ Common Consequences
Section HelpThis 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.
ScopeImpactLikelihood
Confidentiality
Other

Technical Impact: Read Application Data; Other

Information exposure.
+ Likelihood Of Exploit
Medium
+ Demonstrative Examples

Example 1

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.

+ Potential Mitigations

Phase: Architecture and Design

Whenever possible, specify implementation strategies that do not introduce time variances in operations.

Phase: Implementation

Often one can artificially manipulate the time which operations take or -- when operations occur -- can remove information from the attacker.

Phase: Implementation

It is reasonable to add artificial or random delays so that the amount of CPU time consumed is independent of the action being taken by the application.
+ Memberships
Section HelpThis 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.
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.968SFP Secondary Cluster: Covert Channel
+ Notes

Maintenance

As of CWE 4.9, members of the CWE Hardware SIG are working to improve CWE's coverage of transient execution weaknesses, which include issues related to Spectre, Meltdown, and other attacks that create or exploit covert channels. As a result of that work, this entry might change in CWE 4.10.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
LandwehrTiming
CLASPCovert Timing Channel
+ References
[REF-18] Secure Software, Inc.. "The CLASP Application Security Process". 2005. <https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf>.
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2006-07-19Landwehr
+ Modifications
Modification DateModifierOrganization
2008-07-01Eric DalciCigital
updated Time_of_Introduction
2008-09-08CWE Content TeamMITRE
updated Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings
2008-10-14CWE Content TeamMITRE
updated Description
2009-07-27CWE Content TeamMITRE
updated Description, Other_Notes, Potential_Mitigations
2010-09-27CWE Content TeamMITRE
updated Common_Consequences, Description
2011-03-29CWE Content TeamMITRE
updated Description
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2012-05-11CWE Content TeamMITRE
updated Related_Attack_Patterns, Relationships
2014-07-30CWE Content TeamMITRE
updated Relationships
2017-11-08CWE Content TeamMITRE
updated Applicable_Platforms, Demonstrative_Examples
2020-02-24CWE Content TeamMITRE
updated References, Relationships
2022-10-13CWE Content TeamMITRE
updated Maintenance_Notes
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Page Last Updated: January 31, 2023