CWE-585 Variant Draft

Empty Synchronized Block

An empty synchronized block is a Java code construct where a synchronized block exists but contains no executable statements inside it.

Definition

What is CWE-585?

An empty synchronized block is a Java code construct where a synchronized block exists but contains no executable statements inside it.
An empty synchronized block is a logic flaw that fails to provide any actual thread safety or mutual exclusion. While the synchronized keyword is present, the block does nothing to protect shared data or coordinate threads, leaving critical sections of your code vulnerable to race conditions and concurrency bugs. This issue often arises during code maintenance, such as when a developer comments out or removes the internal logic for debugging but forgets to remove the now-useless synchronization wrapper. It serves as a clear red flag for developers to review that section of code, as it either indicates missing functionality or unnecessary overhead that can harm performance without benefit.
Real-world impact

Real-world CVEs caused by CWE-585

No public CVE references are linked to this CWE in MITRE's catalog yet.

How attackers exploit it

Step-by-step attacker path

  1. 1

    Identify a code path that handles untrusted input without validation.

  2. 2

    Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.

  3. 3

    Deliver the payload through a normal request and observe the application's reaction.

  4. 4

    Iterate until the response leaks data, executes attacker code, or escalates privileges.

Vulnerable code example

Vulnerable Java

The following code attempts to synchronize on an object, but does not execute anything in the synchronized block. This does not actually accomplish anything and may be a sign that a programmer is wrestling with synchronization but has not yet achieved the result they intend.

Vulnerable Java 
synchronized(this) { }
Secure code example

Secure Java

Instead, in a correct usage, the synchronized statement should contain procedures that access or modify data that is exposed to multiple threads. For example, consider a scenario in which several threads are accessing student records at the same time. The method which sets the student ID to a new value will need to make sure that nobody else is accessing this data at the same time and will require synchronization.

Secure Java 
public void setID(int ID){
  	synchronized(this){
  		this.ID = ID;
  	}
  }
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-585

  • Implementation When you come across an empty synchronized statement, or a synchronized statement in which the code has been commented out, try to determine what the original intentions were and whether or not the synchronized block is still necessary.
Detection signals

How to detect CWE-585

Automated Static Analysis High

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

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Frequently asked questions

Frequently asked questions

What is CWE-585?

An empty synchronized block is a Java code construct where a synchronized block exists but contains no executable statements inside it.

How serious is CWE-585?

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-585?

MITRE lists the following affected platforms: Java.

How can I prevent CWE-585?

When you come across an empty synchronized statement, or a synchronized statement in which the code has been commented out, try to determine what the original intentions were and whether or not the synchronized block is still necessary.

How does Plexicus detect and fix CWE-585?

Plexicus's SAST engine matches the data-flow signature for CWE-585 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-585?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/585.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-585

CWE-1071 Parent

Empty Code Block

An empty code block occurs when a section of source code, such as a conditional statement or function body, contains no executable…

CWE-1069 Sibling

Empty Exception Block

This weakness occurs when a try-catch or try-finally block is present but contains no code to handle the caught exception or perform…

Resources

Further reading

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