CWE-820 Base Incomplete

Missing Synchronization

This vulnerability occurs when multiple parts of your application (like threads or processes) use the same resource—such as a variable, file, or data structure—without proper coordination to control…

Definition

What is CWE-820?

This vulnerability occurs when multiple parts of your application (like threads or processes) use the same resource—such as a variable, file, or data structure—without proper coordination to control who accesses it and when.
When different parts of your code run concurrently and touch a shared resource without synchronization, the resource's state can become unpredictable. One thread might read a value while another is halfway through modifying it, or two processes might overwrite each other's changes, leading to corrupted data, crashes, or incorrect calculations that break your application's logic. This lack of coordination creates a race condition window that attackers can potentially exploit. By carefully timing their interactions, an attacker might manipulate the shared resource into an unexpected state that bypasses security checks, leaks sensitive information, or causes the system to behave in unintended and insecure ways.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-820

Bisher sind in MITREs Katalog keine öffentlichen CVE-Referenzen mit dieser CWE verknüpft.

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

  1. 1

    The following code intends to fork a process, then have both the parent and child processes print a single line.

  2. 2

    One might expect the code to print out something like:

  3. 3

    ``` PARENT child ```

  4. 4

    However, because the parent and child are executing concurrently, and stdout is flushed each time a character is printed, the output might be mixed together, such as:

  5. 5

    ``` PcAhRiElNdT [blank line] [blank line] ```

Verwundbares Codebeispiel

Vulnerable C

The following code intends to fork a process, then have both the parent and child processes print a single line.

Verwundbar C 
static void print (char * string) {
  		char * word;
  		int counter;
  		for (word = string; counter = *word++; ) {
  				putc(counter, stdout);
  				fflush(stdout);
```
/* Make timing window a little larger... */* 
  				
  				sleep(1);}}
  
  int main(void) {
  ```
  		pid_t pid;
  		pid = fork();
  		if (pid == -1) {
  			exit(-2);
  		}
  		else if (pid == 0) {
  			print("child\n");
  		}
  		else {
  			print("PARENT\n");
  		}
  		exit(0);
  }
Sicheres Codebeispiel

Secure pseudo

Sicher 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.
Präventions-Checkliste

How to prevent CWE-820

  • 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.
Erkennungssignale

How to detect CWE-820

SAST High

Führe statische Analyse (SAST) auf der Codebasis aus und suche im Datenfluss nach dem unsicheren Muster.

DAST Moderate

Führe dynamische Application-Security-Tests gegen den Live-Endpoint aus.

Runtime Moderate

Beobachte Runtime-Logs auf ungewöhnliche Exception-Traces, fehlerhafte Eingaben oder Versuche, Autorisierung zu umgehen.

Code review Moderate

Code Review: Markiere jeden neuen Code, der Eingaben von dieser Oberfläche ohne validierte Framework-Helper verarbeitet.

Plexicus Auto-Fix

Plexicus erkennt CWE-820 automatisch und öffnet in unter 60 Sekunden einen Fix-PR.

Codex Remedium scannt jeden Commit, identifiziert genau diese Schwachstelle und liefert einen reviewer-ready Pull Request mit dem Patch. Keine Tickets. Keine Hand-offs.

Demo anfordern Plexicus kostenlos testen
Häufig gestellte Fragen

Frequently asked questions

Was ist CWE-820?

This vulnerability occurs when multiple parts of your application (like threads or processes) use the same resource—such as a variable, file, or data structure—without proper coordination to control who accesses it and when.

Wie gravierend ist CWE-820?

MITRE hat für diese Schwachstelle keine Exploit-Wahrscheinlichkeit veröffentlicht. Behandle sie als mittlere Auswirkung, bis dein Threat Model anderes belegt.

Welche Sprachen oder Plattformen sind von CWE-820 betroffen?

MITRE hat für diese CWE keine betroffenen Plattformen spezifiziert — sie kann in den meisten Anwendungs-Stacks auftreten.

Wie kann ich CWE-820 verhindern?

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.

Wie erkennt und behebt Plexicus CWE-820?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-820 bei jedem Commit. Bei einem Treffer öffnet unser Codex-Remedium-Agent einen Fix-PR mit korrigiertem Code, Tests und einer einzeiligen Zusammenfassung für den Reviewer.

Wo erfahre ich mehr über CWE-820?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/820.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-820

CWE-662 Parent

Improper Synchronization

This vulnerability occurs when a multi-threaded or multi-process application allows shared resources to be accessed by multiple threads or…

CWE-1058 Sibling

Invokable Control Element in Multi-Thread Context with non-Final Static Storable or Member Element

This happens when a method or function, designed to run in a multi-threaded environment, accesses or modifies a non-final static variable…

CWE-1096 Sibling

Singleton Class Instance Creation without Proper Locking or Synchronization

This flaw occurs when a Singleton class is implemented without proper thread-safe controls, allowing multiple instances to be created in…

CWE-366 Sibling

Race Condition within a Thread

This vulnerability occurs when two or more threads within the same application access and manipulate a shared resource (like a variable,…

CWE-543 Sibling

Use of Singleton Pattern Without Synchronization in a Multithreaded Context

This vulnerability occurs when a singleton pattern is implemented in a multithreaded application without proper synchronization,…

CWE-567 Sibling

Unsynchronized Access to Shared Data in a Multithreaded Context

This vulnerability occurs when multiple threads in an application can read and modify shared data, like static variables, without proper…

CWE-663 Sibling

Use of a Non-reentrant Function in a Concurrent Context

This vulnerability occurs when a program uses a function that is not safe for reentrancy within a concurrent environment, such as…

CWE-667 Sibling

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-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…

Ressourcen

Further reading

Bereit, wenn du es bist

Schluss mit dem Bezahlen pro Entwickler.
Schließ den Kreislauf.

Plexicus ist die KI-native ASPM, die scannt, filtert, fixt, pentestet und erklärt — autonom. Unbegrenzte Entwickler, unbegrenzte Repos, Fair-Use-KI-Aktionen. Echter kostenloser Tarif, €269/mo jährlich, wenn du bereit bist.

Kostenlos starten Demo buchen