CWE-499 Variant Draft High likelihood

Serializable Class Containing Sensitive Data

This vulnerability occurs when a class containing sensitive information, such as credentials or personal data, is left serializable by default. Because the class does not explicitly prevent…

Definition

What is CWE-499?

This vulnerability occurs when a class containing sensitive information, such as credentials or personal data, is left serializable by default. Because the class does not explicitly prevent serialization, its internal data can be accessed and extracted by other parts of the application or external processes.
When a class implements Serializable without safeguards, it effectively becomes an open book. The sensitive fields within it cannot be truly hidden; any other class with serialization access can reconstruct the object and read its private data, bypassing intended access controls. This exposes critical information that should remain protected. To prevent this, developers should explicitly deny serialization for sensitive classes by marking them as 'transient' or overriding serialization methods. While SAST tools can detect this pattern, Plexicus uses AI to not only identify the flaw but also generate the specific code fix—such as adding a custom `readObject` method—saving significant manual remediation time across your codebase.
Real-world impact

Real-world CVEs caused by CWE-499

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 code creates a new record for a medical patient:

Vulnerable Java 
class PatientRecord {
  	private String name;
  	private String socialSecurityNum;
  	public Patient(String name,String ssn) {
  		this.SetName(name);
  		this.SetSocialSecurityNumber(ssn);
  	}
  }
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-499

  • Implementation In Java, explicitly define final writeObject() to prevent serialization. This is the recommended solution. Define the writeObject() function to throw an exception explicitly denying serialization.
  • Implementation Make sure to prevent serialization of your objects.
Detection signals

How to detect CWE-499

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.)

Plexicus auto-fix

Plexicus auto-detects CWE-499 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-499?

This vulnerability occurs when a class containing sensitive information, such as credentials or personal data, is left serializable by default. Because the class does not explicitly prevent serialization, its internal data can be accessed and extracted by other parts of the application or external processes.

How serious is CWE-499?

MITRE rates the likelihood of exploit as High — this weakness is actively exploited in the wild and should be prioritized for remediation.

What languages or platforms are affected by CWE-499?

MITRE lists the following affected platforms: Java.

How can I prevent CWE-499?

In Java, explicitly define final writeObject() to prevent serialization. This is the recommended solution. Define the writeObject() function to throw an exception explicitly denying serialization. Make sure to prevent serialization of your objects.

How does Plexicus detect and fix CWE-499?

Plexicus's SAST engine matches the data-flow signature for CWE-499 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-499?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/499.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-499

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CWE-1327 Sibling

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CWE-1331 Sibling

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CWE-134 Sibling

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CWE-200 Sibling

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CWE-374 Sibling

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CWE-375 Sibling

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