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-766 Base Incomplete
Critical Data Element Declared Public
This vulnerability occurs when a critical piece of data—like a variable, field, or class member—is mistakenly declared as public when it should be kept private according to the application's…
Definition
What is CWE-766?
This vulnerability occurs when a critical piece of data—like a variable, field, or class member—is mistakenly declared as public when it should be kept private according to the application's security design.
Declaring sensitive data as public breaks fundamental security principles like encapsulation and least privilege. It directly exposes critical information, such as internal state, configuration secrets, or authentication tokens, to any other part of the codebase or, in some languages and contexts, to external actors. This creates a clear and immediate attack surface, making it trivial for an attacker to read or modify data that should be strictly controlled.
Beyond the direct security flaw, this practice severely damages code maintainability and security hygiene. It becomes difficult to track how and where this critical data is being used or altered, scattering logic that should be centralized. This "spaghetti code" effect makes identifying the root cause of bugs or vulnerabilities more time-consuming and increases the risk of introducing new security weaknesses during future development or refactoring.
Real-world impact
Real-world CVEs caused by CWE-766
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variables declared public allow remote read of system properties such as user name and home directory.
How attackers exploit it
Step-by-step attacker path
- 1
The following example declares a critical variable public, making it accessible to anyone with access to the object in which it is contained.
- 2
Instead, the critical data should be declared private.
- 3
Even though this example declares the password to be private, there are other possible issues with this implementation, such as the possibility of recovering the password from process memory (CWE-257).
- 4
The following example shows a basic user account class that includes member variables for the username and password as well as a public constructor for the class and a public method to authorize access to the user account.
- 5
However, the member variables username and password are declared public and therefore will allow access and changes to the member variables to anyone with access to the object. These member variables should be declared private as shown below to prevent unauthorized access and changes.
Vulnerable code example
Vulnerable C++
The following example declares a critical variable public, making it accessible to anyone with access to the object in which it is contained.
public: char* password; Secure code example
Secure C++
Instead, the critical data should be declared private.
private: char* password; 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-766
- Implementation Data should be private, static, and final whenever possible. This will assure that your code is protected by instantiating early, preventing access, and preventing tampering.
Detection signals
How to detect CWE-766
Plexicus auto-detects CWE-766 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.
Frequently asked questions What is CWE-766?
How serious is CWE-766?
What languages or platforms are affected by CWE-766?
How can I prevent CWE-766?
How does Plexicus detect and fix CWE-766?
Where can I learn more about CWE-766?
Frequently asked questions
What is CWE-766?
This vulnerability occurs when a critical piece of data—like a variable, field, or class member—is mistakenly declared as public when it should be kept private according to the application's security design.
How serious is CWE-766?
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-766?
MITRE lists the following affected platforms: C++, C#, Java.
How can I prevent CWE-766?
Data should be private, static, and final whenever possible. This will assure that your code is protected by instantiating early, preventing access, and preventing tampering.
How does Plexicus detect and fix CWE-766?
Plexicus's SAST engine matches the data-flow signature for CWE-766 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-766?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/766.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-766
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Insecure Inherited Permissions
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Insecure Preserved Inherited Permissions
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CWE-279 Sibling
Incorrect Execution-Assigned Permissions
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CWE-281 Sibling
Improper Preservation of Permissions
This vulnerability occurs when a system fails to correctly maintain file or object permissions during operations like copying, sharing, or…
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