CWE-767 Base Incomplete

Access to Critical Private Variable via Public Method

This vulnerability occurs when a class exposes a public method that directly accesses or alters a private variable.

Definition

What is CWE-767?

This vulnerability occurs when a class exposes a public method that directly accesses or alters a private variable.
Exposing a private variable through a public method breaks a core principle of encapsulation. It allows external code, including potential attacker-controlled inputs, to bypass intended controls and directly manipulate sensitive internal data. This can lead to the variable holding values the rest of the codebase never expects, corrupting the application's state and violating critical security assumptions. Beyond unexpected modification, this flaw can also lead to information disclosure. An attacker might use the public method to read the private variable's contents, potentially leaking sensitive data like internal flags, cryptographic keys, or user information. This exposed data not only compromises confidentiality but can also provide attackers with the insights needed to craft more sophisticated and targeted follow-up attacks.
Real-world impact

Real-world CVEs caused by CWE-767

No public CVE references are linked to this CWE in MITRE's catalog yet.

How attackers exploit it

Step-by-step attacker path

  1. 1

    The following example declares a critical variable to be private, and then allows the variable to be modified by public methods.

  2. 2

    The following example could be used to implement a user forum where a single user (UID) can switch between multiple profiles (PID).

  3. 3

    The programmer implemented setPID with the intention of modifying the PID variable, but due to a typo. accidentally specified the critical variable UID instead. If the program allows profile IDs to be between 1 and 10, but a UID of 1 means the user is treated as an admin, then a user could gain administrative privileges as a result of this typo.

Vulnerable code example

Vulnerable C++

The following example declares a critical variable to be private, and then allows the variable to be modified by public methods.

Vulnerable C++ 
private: float price;
  public: void changePrice(float newPrice) {
  	price = newPrice;
  }
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-767

  • Implementation Use class accessor and mutator methods appropriately. Perform validation when accepting data from a public method that is intended to modify a critical private variable. Also be sure that appropriate access controls are being applied when a public method interfaces with critical data.
Detection signals

How to detect CWE-767

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-767 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.

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Frequently asked questions

Frequently asked questions

What is CWE-767?

This vulnerability occurs when a class exposes a public method that directly accesses or alters a private variable.

How serious is CWE-767?

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-767?

MITRE lists the following affected platforms: C++, C#, Java.

How can I prevent CWE-767?

Use class accessor and mutator methods appropriately. Perform validation when accepting data from a public method that is intended to modify a critical private variable. Also be sure that appropriate access controls are being applied when a public method interfaces with critical data.

How does Plexicus detect and fix CWE-767?

Plexicus's SAST engine matches the data-flow signature for CWE-767 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-767?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/767.html. You can also reference OWASP and NIST documentation for adjacent guidance.

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Weaknesses related to CWE-767

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CWE-374 Sibling

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Further reading

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