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
The following example declares a critical variable to be private, and then allows the variable to be modified by public methods.
2
The following example could be used to implement a user forum where a single user (UID) can switch between multiple profiles (PID).
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

// 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.

CWE-767

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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.

Related weaknesses

Weaknesses related to CWE-767

CWE-668 Parent

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Access to Critical Private Variable via Public Method

What is CWE-767?

Real-world CVEs caused by CWE-767

Step-by-step attacker path

Vulnerable C++

Secure pseudo

How to prevent CWE-767

How to detect CWE-767

Don't catalog this weakness. Prove it's reachable.

Frequently asked questions

Weaknesses related to CWE-767

Exposure of Resource to Wrong Sphere

Improper Isolation of Shared Resources on System-on-a-Chip (SoC)

Assumed-Immutable Data is Stored in Writable Memory

Binding to an Unrestricted IP Address

Improper Isolation of Shared Resources in Network On Chip (NoC)

Use of Externally-Controlled Format String

Exposure of Sensitive Information to an Unauthorized Actor

Passing Mutable Objects to an Untrusted Method

Returning a Mutable Object to an Untrusted Caller

Further reading

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Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`