CWE-833 Base Incomplete

Deadlock

Deadlock occurs when two or more threads or processes become permanently stuck, each waiting for the other to release a shared resource like a lock or mutex, preventing any of them from progressing.

Definition

What is CWE-833?

Deadlock occurs when two or more threads or processes become permanently stuck, each waiting for the other to release a shared resource like a lock or mutex, preventing any of them from progressing.
Deadlock is a common concurrency bug that arises when threads or processes enter a circular waiting pattern. For example, Thread A holds Lock 1 and waits for Lock 2, while Thread B holds Lock 2 and waits for Lock 1. Since neither can proceed without the resource the other holds, the entire system grinds to a halt. This often stems from inconsistent or poorly managed locking order across different parts of the code. To prevent deadlocks, developers should enforce a strict, global order for acquiring multiple locks and use timeouts or non-blocking lock attempts. Techniques like lock hierarchies, deadlock detection algorithms, and minimizing the scope and duration of locks are crucial. Understanding and managing these dependencies is essential for building robust, multi-threaded applications that avoid this silent failure state.
Real-world impact

Real-world CVEs caused by CWE-833

  • CVE-1999-1476

    A bug in some Intel Pentium processors allow DoS (hang) via an invalid "CMPXCHG8B" instruction, causing a deadlock

  • CVE-2009-2857

    OS deadlock

  • CVE-2009-1961

    OS deadlock involving 3 separate functions

  • CVE-2009-2699

    deadlock in library

  • CVE-2009-4272

    deadlock triggered by packets that force collisions in a routing table

  • CVE-2002-1850

    read/write deadlock between web server and script

  • CVE-2004-0174

    web server deadlock involving multiple listening connections

  • CVE-2009-1388

    multiple simultaneous calls to the same function trigger deadlock.

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 pseudo

MITRE has not published a code example for this CWE. The pattern below is illustrative — see Resources for canonical references.

Vulnerable pseudo 
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
  // Untrusted input flows directly into the sensitive sink.
  return executeUnsafe(input);
}
Secure code example

Secure pseudo

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-833

  • Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
  • Implementation Validate input at trust boundaries; use allowlists, not denylists.
  • Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
  • Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
  • Operation Monitor logs for the runtime signals listed in the next section.
Detection signals

How to detect CWE-833

SAST High

Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.

DAST Moderate

Run dynamic application security testing against the live endpoint.

Runtime Moderate

Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.

Code review Moderate

Code review: flag any new code that handles input from this surface without using the validated framework helpers.

Plexicus auto-fix

Plexicus auto-detects CWE-833 and opens a fix PR in under 60 seconds.

Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.

Get a demo Try Plexicus free
Frequently asked questions

Frequently asked questions

What is CWE-833?

Deadlock occurs when two or more threads or processes become permanently stuck, each waiting for the other to release a shared resource like a lock or mutex, preventing any of them from progressing.

How serious is CWE-833?

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-833?

MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.

How can I prevent CWE-833?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

How does Plexicus detect and fix CWE-833?

Plexicus's SAST engine matches the data-flow signature for CWE-833 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-833?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/833.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-833

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-412 Sibling

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…

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…

Resources

Further reading

Ready when you are

Don't Let Security
Weigh You Down.

Stop choosing between AI velocity and security debt. Plexicus is the only platform that runs Vibe Coding Security and ASPM in parallel — one workflow, every codebase.