CWE-1235: Incorrect Use of Autoboxing and Unboxing for Performance Critical Operations

Definition

What is CWE-1235?

This weakness occurs when a program relies on automatic boxing and unboxing of primitive types within performance-sensitive code sections, causing unnecessary computational overhead and potential resource strain.

Languages like Java and C# provide autoboxing (converting a primitive like `int` to an object like `Integer`) and unboxing (the reverse) to simplify code by handling conversions automatically. While convenient for general use, these operations secretly create new objects and add processing steps that degrade execution speed, especially inside tight loops or high-frequency operations. Using boxed primitives within generic collections or performance-critical areas—such as scientific computing, real-time processing, or low-latency systems—can lead to excessive memory allocation, increased garbage collection, and even resource exhaustion. This practice is best reserved only for bridging the gap between primitive APIs and object-based libraries, not for core computational logic where efficiency is paramount.

Real-world impact

Real-world CVEs caused by CWE-1235

No public CVE references are linked to this CWE in MITRE's catalog yet.

How attackers exploit it

Step-by-step attacker path

1
Java has a boxed primitive for each primitive type. A long can be represented with the boxed primitive Long. Issues arise where boxed primitives are used when not strictly necessary.
2
In the above loop, we see that the count variable is declared as a boxed primitive. This causes autoboxing on the line that increments. This causes execution to be magnitudes less performant (time and possibly space) than if the "long" primitive was used to declare the count variable, which can impact availability of a resource.
3
This code uses primitive long which fixes the issue.

Vulnerable code example

Vulnerable Java

Java has a boxed primitive for each primitive type. A long can be represented with the boxed primitive Long. Issues arise where boxed primitives are used when not strictly necessary.

Vulnerable Java

Long count = 0L; 
   for (long i = 0; i < Integer.MAX_VALUE; i++) { 
  	 count += i; 
   }

Secure code example

Secure Java

This code uses primitive long which fixes the issue.

Secure Java

long count = 0L; 
   for (long i = 0; i < Integer.MAX_VALUE; i++) { 
  	 count += i; 
   }

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-1235

Implementation Use of boxed primitives should be limited to certain situations such as when calling methods with typed parameters. Examine the use of boxed primitives prior to use. Use SparseArrays or ArrayMap instead of HashMap to avoid performance overhead.

Detection signals

How to detect CWE-1235

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-1235

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Frequently asked questions

What is CWE-1235?

This weakness occurs when a program relies on automatic boxing and unboxing of primitive types within performance-sensitive code sections, causing unnecessary computational overhead and potential resource strain.

How serious is CWE-1235?

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-1235?

MITRE lists the following affected platforms: Java, C#, Not OS-Specific, Not Architecture-Specific, Not Technology-Specific.

How can I prevent CWE-1235?

Use of boxed primitives should be limited to certain situations such as when calling methods with typed parameters. Examine the use of boxed primitives prior to use. Use SparseArrays or ArrayMap instead of HashMap to avoid performance overhead.

How does Plexicus detect and fix CWE-1235?

Plexicus's SAST engine matches the data-flow signature for CWE-1235 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-1235?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/1235.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-1235

CWE-400 Parent

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Incorrect Use of Autoboxing and Unboxing for Performance Critical Operations

What is CWE-1235?

Real-world CVEs caused by CWE-1235

Step-by-step attacker path

Vulnerable Java

Secure Java

How to prevent CWE-1235

How to detect CWE-1235

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

Frequently asked questions

Weaknesses related to CWE-1235

Uncontrolled Resource Consumption

Improper Write Handling in Limited-write Non-Volatile Memories

Asymmetric Resource Consumption (Amplification)

Allocation of Resources Without Limits or Throttling

Missing Reference to Active Allocated Resource

Logging of Excessive Data

Improper Restriction of Power Consumption

Further reading

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Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`