CWE-567: Unsynchronized Access to Shared Data in a Multithreaded Context

Extended Description

Within servlets, shared static variables are not protected from concurrent access, but servlets are multithreaded. This is a typical programming mistake in J2EE applications, since the multithreading is handled by the framework. When a shared variable can be influenced by an attacker, one thread could wind up modifying the variable to contain data that is not valid for a different thread that is also using the data within the variable. Note that this weakness is not unique to servlets.

Code Examples & CVEs

Demonstrative Examples

The following code implements a basic counter for how many times the page has been accesed.

Consider when two separate threads, Thread A and Thread B, concurrently handle two different requests:

BadJava

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!");}}

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-567 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-567, Unsynchronized Access to Shared Data in a Multithreaded Context, throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Address Unsynchronized Access to Shared Data in a Multithreaded Context during Implementation

MITRE associates mitigation with Implementation; documented detection approaches include Automated Static Analysis; recorded impacts include Read Application Data, Modify Application Data, DoS: Instability, and DoS: Crash, Exit, or Restart. Use these source-defined anchors to turn CWE-567 into implementation, review, and verification checks for the affected component.

CWE-567: Unsynchronized Access to Shared Data in a Multithreaded Context — MITRE CWE

Triage CWE-567 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-567, Unsynchronized Access to Shared Data in a Multithreaded Context, has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Apply precise root-cause mapping to CWE-567

Apply MITRE's full root-cause mapping guidance when using CWE-567, Unsynchronized Access to Shared Data in a Multithreaded Context. Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-567 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-567, Unsynchronized Access to Shared Data in a Multithreaded Context. Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE CWE

Frequently Asked Questions

What is CWE-567: Unsynchronized Access to Shared Data in a Multithreaded Context?+

CWE-567: Unsynchronized Access to Shared Data in a Multithreaded Context is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product does not properly synchronize shared data, such as static variables across threads, which can lead to undefined behavior and unpredictable data changes. Within servlets, shared static variables are not protected from concurrent access, but servlets are multithreaded. This is a typical programming mistake in J2EE applications, since the multithreading is handled by the framework. When a shared variable can be influenced by an attacker, one thread could wind up modifying the variable to contain data that is not valid for a different thread that is also using the data within the variable. Note that this weakness is not unique to servlets.

What are the security consequences of Unsynchronized Access to Shared Data in a Multithreaded Context?+

If exploited, CWE-567 (Unsynchronized Access to Shared Data in a Multithreaded Context) it can compromise Confidentiality, Integrity and Availability, leading to outcomes such as Read Application Data, Modify Application Data, DoS: Instability and DoS: Crash, Exit, or Restart.

How do you prevent or mitigate Unsynchronized Access to Shared Data in a Multithreaded Context?+

Recommended mitigations for CWE-567 include: Remove the use of static variables used between servlets. If this cannot be avoided, use synchronized access for these variables.

Which programming languages are affected by Unsynchronized Access to Shared Data in a Multithreaded Context?+

CWE-567 commonly affects Java. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-567 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.

CWE-567: Unsynchronized Access to Shared Data in a Multithreaded Context

Extended Description

Technical Details

Applicable To

Security Consequences

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