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.
CWE-412 Base Incomplete
Unrestricted Externally Accessible Lock
This vulnerability occurs when a system correctly checks for a lock's existence, but an unauthorized external actor can control or influence that lock.
Definition
What is CWE-412?
This vulnerability occurs when a system correctly checks for a lock's existence, but an unauthorized external actor can control or influence that lock.
When an attacker can manipulate a lock—such as a mutex, file lock, or a shared resource used as a lock—they can prevent the application from accessing critical resources or performing essential operations. This effectively creates a denial-of-service condition, as the system remains blocked waiting for a lock it cannot acquire.
The severity of this issue escalates if the attacker can hold the lock indefinitely, leading to a permanent disruption of service. Developers must ensure that lock mechanisms are secured within the application's trusted boundary and cannot be created, modified, or sustained by untrusted external sources.
Real-world impact
Real-world CVEs caused by CWE-412
-
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.
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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.
How attackers exploit it
Step-by-step attacker path
- 1
Identify a code path that handles untrusted input without validation.
- 2
Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.
- 3
Deliver the payload through a normal request and observe the application's reaction.
- 4
Iterate until the response leaks data, executes attacker code, or escalates privileges.
Vulnerable code example
Vulnerable PHP
This code tries to obtain a lock for a file, then writes to it.
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); Secure code example
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist
How to prevent CWE-412
- 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 signals
How to detect CWE-412
CWE-412
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Frequently asked questions What is CWE-412?
How serious is CWE-412?
What languages or platforms are affected by CWE-412?
How can I prevent CWE-412?
How does Plexicus detect and fix CWE-412?
Where can I learn more about CWE-412?
Frequently asked questions
What is CWE-412?
This vulnerability occurs when a system correctly checks for a lock's existence, but an unauthorized external actor can control or influence that lock.
How serious is CWE-412?
MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.
What languages or platforms are affected by CWE-412?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent CWE-412?
Use any access control that is offered by the functionality that is offering the lock. Use unpredictable names or identifiers for the locks. This might not always be possible or feasible.
How does Plexicus detect and fix CWE-412?
Plexicus's SAST engine matches the data-flow signature for CWE-412 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-412?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/412.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-412
CWE-667 Parent
Improper Locking
This vulnerability occurs when a program fails to correctly acquire or release a lock on a shared resource, such as a file, database…
CWE-1232 Sibling
Improper Lock Behavior After Power State Transition
This vulnerability occurs when a hardware lock bit, designed to protect critical system configuration registers, is improperly reset or…
CWE-1233 Sibling
Security-Sensitive Hardware Controls with Missing Lock Bit Protection
This vulnerability occurs when a hardware device uses a lock bit to protect critical configuration registers, but the lock fails to…
CWE-1234 Sibling
Hardware Internal or Debug Modes Allow Override of Locks
Hardware debug modes or internal states can bypass critical system lock protections, allowing unauthorized changes to device configuration.
CWE-413 Sibling
Improper Resource Locking
This vulnerability occurs when an application fails to properly lock a shared resource, such as a file or memory location, before…
CWE-414 Sibling
Missing Lock Check
This vulnerability occurs when software fails to verify that a proper synchronization lock is active before accessing or modifying a…
CWE-609 Sibling
Double-Checked Locking
Double-checked locking is an insufficient synchronization pattern where a program checks a resource's state, acquires a lock, and checks…
CWE-764 Sibling
Multiple Locks of a Critical Resource
This vulnerability occurs when a critical resource, such as a file, data structure, or connection, is locked more times than the software…
CWE-765 Sibling
Multiple Unlocks of a Critical Resource
This vulnerability occurs when a critical resource, like a lock or semaphore, is unlocked more times than it was locked, putting the…
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