CWE-375: Returning a Mutable Object to an Untrusted Caller

Extended Description

In situations where functions return references to mutable data, it is possible that the external code which called the function may make changes to the data sent. If this data was not previously cloned, the class will then be using modified data which may violate assumptions about its internal state.

Code Examples & CVEs

Demonstrative Examples

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

While this code only means to allow reading of the patient list, the getPatients() method returns a reference to the class's original patient list instead of a reference to a copy of the list. Any caller of this method can arbitrarily modify the contents of the patient list even though it is a private member of the class.

BadJava

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

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-375 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-375, Returning a Mutable Object to an Untrusted Caller, 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 Returning a Mutable Object to an Untrusted Caller during Implementation

MITRE associates mitigation with Implementation; recorded impacts include Modify Memory; related weaknesses include CWE-668. Use these source-defined anchors to turn CWE-375 into implementation, review, and verification checks for the affected component.

CWE-375: Returning a Mutable Object to an Untrusted Caller — MITRE CWE

Triage CWE-375 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-375, Returning a Mutable Object to an Untrusted Caller, 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-375

Apply MITRE's full root-cause mapping guidance when using CWE-375, Returning a Mutable Object to an Untrusted Caller. 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-375 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-375, Returning a Mutable Object to an Untrusted Caller. 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-375: Returning a Mutable Object to an Untrusted Caller?+

CWE-375: Returning a Mutable Object to an Untrusted Caller is a Common Weakness Enumeration (CWE) entry maintained by MITRE. Sending non-cloned mutable data as a return value may result in that data being altered or deleted by the calling function. In situations where functions return references to mutable data, it is possible that the external code which called the function may make changes to the data sent. If this data was not previously cloned, the class will then be using modified data which may violate assumptions about its internal state.

What are the security consequences of Returning a Mutable Object to an Untrusted Caller?+

If exploited, CWE-375 (Returning a Mutable Object to an Untrusted Caller) it can compromise Access Control and Integrity, leading to outcomes such as Modify Memory.

How do you prevent or mitigate Returning a Mutable Object to an Untrusted Caller?+

Recommended mitigations for CWE-375 include: 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.

Which programming languages are affected by Returning a Mutable Object to an Untrusted Caller?+

CWE-375 commonly affects C, C++, Java, C# and Object-Oriented. 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-375 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-375: Returning a Mutable Object to an Untrusted Caller

Extended Description

Technical Details

Applicable To

Security Consequences

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Mitigation Strategies

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