CWE-412: Unrestricted Externally Accessible Lock
Official CWE-412 CWE context with Glexia analysis, remediation guidance, related CVEs, and ATT&CK context.
Glexia's Take
CWE-412: Unrestricted Externally Accessible Lock
Unrestricted Externally Accessible Lock represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Executive Impact
- Availability: 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.
Developer Pattern
CWE-412 is the kind of defect developers can usually prevent with explicit validation, safer framework defaults, and tests that exercise hostile input or unsafe state transitions.
Confidence
high confidence from CWE-412, 4.20.
Official CWE Definition
CWE-412: Unrestricted Externally Accessible Lock
The product 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.
This prevents the product 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.
Developer And Remediation Guidance
How teams prevent and detect this weakness
Causes
- This code tries to obtain a lock for a file, then writes to it. 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().
Remediation
- Architecture and Design,Implementation: Use any access control that is offered by the functionality that is offering the lock.
- Architecture and Design,Implementation: Use unpredictable names or identifiers for the locks. This might not always be possible or feasible.
- Architecture and Design: Consider modifying your code to use non-blocking synchronization methods.
Detection
- 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.
Mappings
Related CVEs, CWEs, and ATT&CK context
ATT&CK Relevance
ATT&CK relevance is shown only when reviewed or responsibly inferred.