CWE-375 Base Draft Medium likelihood

Returning a Mutable Object to an Untrusted Caller

This vulnerability occurs when a method directly returns a reference to its internal mutable data, allowing untrusted calling code to modify that data unexpectedly.

Definition

What is CWE-375?

This vulnerability occurs when a method directly returns a reference to its internal mutable data, allowing untrusted calling code to modify that data unexpectedly.
When a function returns a reference to an object like an array, collection, or custom data structure without making a defensive copy, the caller gains the power to change the object's contents. Since both the class and the caller hold references to the same underlying data, any modifications made by the caller directly alter the class's internal state. This breaks a core principle of encapsulation, as the class can no longer control or guarantee the integrity of its own data. To prevent this, methods should never return direct references to mutable internal fields. Instead, return a deep copy of the data or an immutable view (like an unmodifiable wrapper). This practice ensures the calling code can use the returned data without being able to corrupt the original object's state, preserving the class's invariants and security.
Real-world impact

Real-world CVEs caused by CWE-375

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

    Identify a code path that handles untrusted input without validation.

  2. 2

    Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.

  3. 3

    Deliver the payload through a normal request and observe the application's reaction.

  4. 4

    Iterate until the response leaks data, executes attacker code, or escalates privileges.

Vulnerable code example

Vulnerable Java

This class has a private list of patients, but provides a way to see the list :

Vulnerable Java 
public class ClinicalTrial {
  	private PatientClass[] patientList = new PatientClass[50];
  	public getPatients(...){
  		return patientList;
  	}
  }
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-375

  • Implementation Declare returned data which should not be altered as constant or immutable.
  • Implementation Clone all mutable data before returning references to it. This is the preferred mitigation. This way, regardless of what changes are made to the data, a valid copy is retained for use by the class.
Detection signals

How to detect CWE-375

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-375 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-375?

This vulnerability occurs when a method directly returns a reference to its internal mutable data, allowing untrusted calling code to modify that data unexpectedly.

How serious is CWE-375?

MITRE rates the likelihood of exploit as Medium — exploitation is realistic but typically requires specific conditions.

What languages or platforms are affected by CWE-375?

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

How can I prevent CWE-375?

Declare returned data which should not be altered as constant or immutable. Clone all mutable data before returning references to it. This is the preferred mitigation. This way, regardless of what changes are made to the data, a valid copy is retained for use by the class.

How does Plexicus detect and fix CWE-375?

Plexicus's SAST engine matches the data-flow signature for CWE-375 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-375?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/375.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-375

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CWE-1189 Sibling

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CWE-1282 Sibling

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CWE-1327 Sibling

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CWE-1331 Sibling

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

This vulnerability occurs when a Network on Chip (NoC) fails to properly separate its internal, shared resources—like buffers, switches,…

CWE-134 Sibling

Use of Externally-Controlled Format String

This vulnerability occurs when a program uses a format string from an untrusted, external source (like user input, a network packet, or a…

CWE-200 Sibling

Exposure of Sensitive Information to an Unauthorized Actor

This weakness occurs when an application unintentionally reveals sensitive data to someone who shouldn't have access to it.

CWE-374 Sibling

Passing Mutable Objects to an Untrusted Method

This vulnerability occurs when a function receives a direct reference to mutable data, such as an object or array, instead of a safe copy…

CWE-377 Sibling

Insecure Temporary File

This vulnerability occurs when an application creates temporary files with insecure permissions or in predictable locations, allowing…

Resources

Further reading

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