CWE

Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

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ID

CWE-412: Unrestricted Externally Accessible Lock

Weakness ID: 412
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The software properly checks for the existence of a lock, but the lock can be externally controlled or influenced by an actor that is outside of the intended sphere of control.
+ Extended Description
This prevents the software from acting on associated resources or performing other behaviors that are controlled by the presence of the lock. Relevant locks might include an exclusive lock or mutex, or modifying a shared resource that is treated as a lock. If the lock can be held for an indefinite period of time, then the denial of service could be permanent.
+ Relationships

The table(s) below 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
ChildOfBaseBase667Improper Locking
CanAlsoBeBaseBase410Insufficient Resource Pool
+ Relevant to the view "Development Concepts" (CWE-699)
NatureTypeIDName
MemberOfCategoryCategory3617PK - Time and State
MemberOfCategoryCategory411Resource Locking Problems
+ 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 software 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
The listings below show 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

(Language-Independent classes): (Undetermined Prevalence)

+ Common Consequences

The table below 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
Availability

Technical Impact: DoS: Resource Consumption (Other)

When an attacker can control a lock, the program may wait indefinitely until the attacker releases the lock, causing a denial of service to other users of the program. This is especially problematic if there is a blocking operation on the lock.
+ Demonstrative Examples

Example 1

This code tries to obtain a lock for a file, then writes to it.

(bad)
Example Language: PHP 
function writeToLog($message){
$logfile = fopen("logFile.log", "a");
//attempt to get logfile lock

if (flock($logfile, LOCK_EX)) {
fwrite($logfile,$message);
// unlock logfile

flock($logfile, LOCK_UN);

}
else {
print "Could not obtain lock on logFile.log, message not recorded\n";

}

}
fclose($logFile);

PHP by default will wait indefinitely until a file lock is released. If an attacker is able to obtain the file lock, this code will pause execution, possibly leading to denial of service for other users. Note that in this case, if an attacker can perform an flock() on the file, they may already have privileges to destroy the log file. However, this still impacts the execution of other programs that depend on flock().

+ Observed Examples
ReferenceDescription
Program can not execute when attacker obtains a mutex.
Program can not execute when attacker obtains a lock on a critical output file.
Program can not execute when attacker obtains a lock on a critical output file.
Critical file can be opened with exclusive read access by user, preventing application of security policy. Possibly related to improper permissions, large-window race condition.
Chain: predictable file names used for locking, allowing attacker to create the lock beforehand. Resultant from permissions and randomness.
Chain: Lock files with predictable names. Resultant from randomness.
Product does not check if it can write to a log file, allowing attackers to avoid logging by accessing the file using an exclusive lock. Overlaps unchecked error condition. This is not quite CWE-412, but close.
+ Potential Mitigations

Phases: Architecture and Design; Implementation

Use any access control that is offered by the functionality that is offering the lock.

Phases: Architecture and Design; Implementation

Use unpredictable names or identifiers for the locks. This might not always be possible or feasible.

Phase: Architecture and Design

Consider modifying your code to use non-blocking synchronization methods.
+ Detection Methods

White Box

Automated code analysis techniques might not be able to reliably detect this weakness, since the application's behavior and general security model dictate which resource locks are critical. Interpretation of the weakness might require knowledge of the environment, e.g. if the existence of a file is used as a lock, but the file is created in a world-writable directory.
+ 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.
+ Notes

Relationship

This overlaps Insufficient Resource Pool when the "pool" is of size 1. It can also be resultant from race conditions, although the timing window could be quite large in some cases.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERUnrestricted Critical Resource Lock
7 Pernicious KingdomsDeadlock
OWASP Top Ten 2004A9CWE More SpecificDenial of Service
CERT Java Secure CodingLCK00-JUse private final lock objects to synchronize classes that may interact with untrusted code
CERT Java Secure CodingLCK07-JAvoid deadlock by requesting and releasing locks in the same order
Software Fault PatternsSFP22Unrestricted lock
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVER
Contributions
Contribution DateContributorOrganizationSource
2008-08-29KDM Analytics
suggested clarification of description and observed examples, which were vague and inconsistent.
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigital
updated Potential_Mitigations, Time_of_Introduction
2008-08-01KDM Analytics
added/updated white box definitions
2008-08-15Veracode
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITRE
updated Common_Consequences, Description, Detection_Factors, Relationships, Observed_Example, Relationship_Notes, Taxonomy_Mappings
2008-10-14CWE Content TeamMITRE
updated Description
2009-07-17KDM Analytics
Suggested a better name and the minimal relationship with resources regardless of their criticality.
2009-07-17KDM Analytics
Added a White_Box_Definition and clarified the consequences.
2009-07-27CWE Content TeamMITRE
updated Common_Consequences, Description, Name, Potential_Mitigations, White_Box_Definitions
2011-03-29CWE Content TeamMITRE
updated Demonstrative_Examples
2011-06-01CWE Content TeamMITRE
updated Common_Consequences, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITRE
updated Demonstrative_Examples, Relationships
2014-07-30CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2017-11-08CWE Content TeamMITRE
updated Applicable_Platforms, Relationships, White_Box_Definitions
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Unrestricted Critical Resource Lock
2009-07-27Unrestricted Lock on Critical Resource

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Page Last Updated: November 14, 2017