CWE-771 Base Incomplete Medium likelihood

Missing Reference to Active Allocated Resource

This vulnerability occurs when software loses track of a resource it has allocated, like memory or a file handle, preventing the system from properly releasing it back for future use.

Definition

What is CWE-771?

This vulnerability occurs when software loses track of a resource it has allocated, like memory or a file handle, preventing the system from properly releasing it back for future use.
This issue, often called a resource leak, happens when a program allocates a resource but then loses all pointers or handles to it. Without an active reference, the developer's code can no longer access or free the resource, yet the system still considers it in use. This slowly drains available system resources, which can lead to performance degradation or crashes. In environments with automatic garbage collection, this problem is less common for memory because the system can reclaim memory once all references are gone. However, garbage collectors often don't manage other resources like database connections, open files, or network sockets, so explicit cleanup is still required for those, making this a relevant concern in most programming contexts.
Real-world impact

Real-world CVEs caused by CWE-771

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-771

  • Operation / Architecture and Design Use resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems. When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users. Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).
Detection signals

How to detect CWE-771

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-771 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-771?

This vulnerability occurs when software loses track of a resource it has allocated, like memory or a file handle, preventing the system from properly releasing it back for future use.

How serious is CWE-771?

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

What languages or platforms are affected by CWE-771?

MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.

How can I prevent CWE-771?

Use resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems. When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged…

How does Plexicus detect and fix CWE-771?

Plexicus's SAST engine matches the data-flow signature for CWE-771 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-771?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/771.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-771

CWE-400 Parent

Uncontrolled Resource Consumption

This vulnerability occurs when an application fails to properly manage a finite resource, allowing an attacker to exhaust it and cause a…

CWE-1235 Sibling

Incorrect Use of Autoboxing and Unboxing for Performance Critical Operations

This weakness occurs when a program relies on automatic boxing and unboxing of primitive types within performance-sensitive code sections,…

CWE-1246 Sibling

Improper Write Handling in Limited-write Non-Volatile Memories

This vulnerability occurs when a system fails to properly manage write operations on memory hardware that has a limited lifespan, such as…

CWE-405 Sibling

Asymmetric Resource Consumption (Amplification)

This vulnerability occurs when a system allows an attacker to trigger a disproportionate amount of resource consumption—like CPU, memory,…

CWE-770 Sibling

Allocation of Resources Without Limits or Throttling

This vulnerability occurs when a system allows users or processes to request resources without any built-in caps or rate limits. Think of…

CWE-779 Sibling

Logging of Excessive Data

This vulnerability occurs when an application records more information than necessary in its logs, making log files difficult to analyze…

CWE-920 Sibling

Improper Restriction of Power Consumption

This vulnerability occurs when software running on a power-constrained device, like a battery-powered mobile or embedded system, fails to…

CWE-773 Child

Missing Reference to Active File Descriptor or Handle

This vulnerability occurs when a program fails to keep track of open files or resources, preventing the system from properly closing and…

Resources

Further reading

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