CWE-581 Variant Draft

Object Model Violation: Just One of Equals and Hashcode Defined

This vulnerability occurs when a Java class defines either the equals() method or the hashCode() method, but not both, breaking a fundamental contract of object equality.

Definition

What is CWE-581?

This vulnerability occurs when a Java class defines either the equals() method or the hashCode() method, but not both, breaking a fundamental contract of object equality.
In Java, the `equals()` and `hashCode()` methods work as a pair to define object identity for collections like `HashMap` and `HashSet`. When you override only one of these methods, you violate a core rule: if two objects are considered equal by the `equals()` method, they must return the same `hashCode()` value. Failing to uphold this contract causes unpredictable behavior in hash-based collections, leading to objects that are 'equal' being stored separately, becoming impossible to retrieve, or causing duplicate entries. To fix this, always override both methods together, ensuring their logic is based on the same set of object attributes. Use your IDE's generator or a library like Lombok to maintain consistency. This ensures your objects behave correctly in all standard Java collections and prevents subtle, hard-to-debug errors in your application's data handling.
Real-world impact

Real-world CVEs caused by CWE-581

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 pseudo

MITRE has not published a code example for this CWE. The pattern below is illustrative — see Resources for canonical references.

Vulnerable pseudo 
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
  // Untrusted input flows directly into the sensitive sink.
  return executeUnsafe(input);
}
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-581

  • Implementation Both Equals() and Hashcode() should be defined.
Detection signals

How to detect CWE-581

Automated Static Analysis High

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.)

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Frequently asked questions

Frequently asked questions

What is CWE-581?

This vulnerability occurs when a Java class defines either the equals() method or the hashCode() method, but not both, breaking a fundamental contract of object equality.

How serious is CWE-581?

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-581?

MITRE lists the following affected platforms: Java.

How can I prevent CWE-581?

Both Equals() and Hashcode() should be defined.

How does Plexicus detect and fix CWE-581?

Plexicus's SAST engine matches the data-flow signature for CWE-581 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-581?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/581.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-581

CWE-573 Parent

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CWE-103 Sibling

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CWE-104 Sibling

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CWE-243 Sibling

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CWE-253 Sibling

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CWE-296 Sibling

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CWE-304 Sibling

Missing Critical Step in Authentication

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CWE-325 Sibling

Missing Cryptographic Step

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CWE-329 Sibling

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Resources

Further reading

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