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.)
CWE-567 Base Draft
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 coordination. This unsynchronized access corrupts data,…
Definition
What is CWE-567?
This vulnerability occurs when multiple threads in an application can read and modify shared data, like static variables, without proper coordination. This unsynchronized access corrupts data, causes crashes, and leads to unpredictable, often security-critical, behavior.
A common example is in Java servlet-based applications, where the framework manages multithreading. Developers might mistakenly treat static variables as safe, forgetting that all servlet threads can access them simultaneously. If an attacker can influence this shared data, one thread could inject invalid or malicious content that another thread then processes, creating a serious security flaw.
This issue is not limited to servlets or J2EE. It's a fundamental concurrency flaw that can appear in any multithreaded environment when developers assume single-threaded execution for shared resources. The core problem is a mismatch: the application uses a multithreaded architecture but fails to implement the necessary safeguards, like locks or atomic operations, to protect its shared state from concurrent modification.
Auswirkungen in der Praxis
Real-world CVEs caused by CWE-567
Bisher sind in MITREs Katalog keine öffentlichen CVE-Referenzen mit dieser CWE verknüpft.
Wie Angreifer es ausnutzen
Angreiferpfad Schritt für Schritt
- 1
The following code implements a basic counter for how many times the page has been accesed.
- 2
Consider when two separate threads, Thread A and Thread B, concurrently handle two different requests:
- 3
- Assume this is the first occurrence of doGet, so the value of count is 0. - doGet() is called within Thread A. - The execution of doGet() in Thread A continues to the point AFTER the value of the count variable is read, then incremented, but BEFORE it is saved back to count. At this stage, the incremented value is 1, but the value of count is 0. - doGet() is called within Thread B, and due to a higher thread priority, Thread B progresses to the point where the count variable is accessed (where it is still 0), incremented, and saved. After the save, count is 1. - Thread A continues. It saves the intermediate, incremented value to the count variable - but the incremented value is 1, so count is "re-saved" to 1.
- 4
At this point, both Thread A and Thread B print that one hit has been seen, even though two separate requests have been processed. The value of count should be 2, not 1.
- 5
While this example does not have any real serious implications, if the shared variable in question is used for resource tracking, then resource consumption could occur. Other scenarios exist.
Verwundbares Codebeispiel
Vulnerable Java
The following code implements a basic counter for how many times the page has been accesed.
public static class Counter extends HttpServlet {
static int count = 0;
protected void doGet(HttpServletRequest in, HttpServletResponse out)
throws ServletException, IOException {
out.setContentType("text/plain");
PrintWriter p = out.getWriter();
count++;
p.println(count + " hits so far!");
}
} Sicheres Codebeispiel
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.
Präventions-Checkliste
How to prevent CWE-567
- Implementation Remove the use of static variables used between servlets. If this cannot be avoided, use synchronized access for these variables.
Erkennungssignale
How to detect CWE-567
CWE-567
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Häufig gestellte Fragen Was ist CWE-567?
Wie gravierend ist CWE-567?
Welche Sprachen oder Plattformen sind von CWE-567 betroffen?
Wie kann ich CWE-567 verhindern?
Wie erkennt und behebt Plexicus CWE-567?
Wo erfahre ich mehr über CWE-567?
Frequently asked questions
Was ist CWE-567?
This vulnerability occurs when multiple threads in an application can read and modify shared data, like static variables, without proper coordination. This unsynchronized access corrupts data, causes crashes, and leads to unpredictable, often security-critical, behavior.
Wie gravierend ist CWE-567?
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-567 betroffen?
MITRE lists the following affected platforms: Java.
Wie kann ich CWE-567 verhindern?
Remove the use of static variables used between servlets. If this cannot be avoided, use synchronized access for these variables.
Wie erkennt und behebt Plexicus CWE-567?
Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-567 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-567?
MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/567.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.
Verwandte Schwachstellen
Weaknesses related to CWE-567
CWE-820 Parent
Missing Synchronization
This vulnerability occurs when multiple parts of your application (like threads or processes) use the same resource—such as a 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-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-488 Kann vorausgehen
Exposure of Data Element to Wrong Session
This vulnerability occurs when an application fails to properly isolate data between different user sessions, allowing information from…
Ressourcen
Further reading
Bereit, das Wesentliche zu validieren?
Bereit zu validieren, was zählt.
Plexicus ist Proof-Driven AppSec: validierte Funde, kontextuelles Verständnis und geprüfte Remediation — in Evidenz verankert, mit Ihnen gescoped.