CWE-401 Variant Draft Medium likelihood

Missing Release of Memory after Effective Lifetime

This vulnerability occurs when a program allocates memory but fails to properly release it after it's no longer needed, causing a gradual accumulation of unused memory that can't be reclaimed by the…

Definition

What is CWE-401?

This vulnerability occurs when a program allocates memory but fails to properly release it after it's no longer needed, causing a gradual accumulation of unused memory that can't be reclaimed by the system.
Memory leaks happen when developers allocate memory (e.g., using `malloc()`, `new`, or similar functions) but neglect to free or delete it once the relevant operation is complete. This often stems from complex control flows, error conditions, or long-running processes where tracking every allocation becomes difficult. Over time, especially in servers or persistent applications, these unreleased blocks accumulate, steadily draining available system memory. This resource exhaustion can lead to severe performance degradation, application instability, or complete crashes when the system runs out of memory. To prevent this, developers must ensure that every allocation has a corresponding, guaranteed release, using techniques like automatic resource management (e.g., smart pointers in C++, try-with-resources in Java), rigorous code reviews, and specialized leak detection tools during testing.
Vulnerability Diagram CWE-401
Memory Leak allocate() p = malloc(N) use(p) no free(p) return early repeat ×N heap usage time
Real-world impact

Real-world CVEs caused by CWE-401

  • CVE-2005-3119

    Memory leak because function does not free() an element of a data structure.

  • CVE-2004-0427

    Memory leak when counter variable is not decremented.

  • CVE-2002-0574

    chain: reference count is not decremented, leading to memory leak in OS by sending ICMP packets.

  • CVE-2005-3181

    Kernel uses wrong function to release a data structure, preventing data from being properly tracked by other code.

  • CVE-2004-0222

    Memory leak via unknown manipulations as part of protocol test suite.

  • CVE-2001-0136

    Memory leak via a series of the same command.

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 C

The following C function leaks a block of allocated memory if the call to read() does not return the expected number of bytes:

Vulnerable C 
char* getBlock(int fd) {
  		char* buf = (char*) malloc(BLOCK_SIZE);
  		if (!buf) {
  			return NULL;
  		}
  		if (read(fd, buf, BLOCK_SIZE) != BLOCK_SIZE) {
  				return NULL;
  		}
  		return buf;
  }
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-401

  • Implementation Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone. For example, glibc in Linux provides protection against free of invalid pointers. When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391]. To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and std::unique_ptr (specified by an upcoming revision of the C++ standard, informally referred to as C++ 1x), or equivalent solutions such as Boost.
  • Architecture and Design Use an abstraction library to abstract away risky APIs. Not a complete solution.
  • Architecture and Design / Build and Compilation The Boehm-Demers-Weiser Garbage Collector or valgrind can be used to detect leaks in code.
Detection signals

How to detect CWE-401

Fuzzing High

Fuzz testing (fuzzing) is a powerful technique for generating large numbers of diverse inputs - either randomly or algorithmically - and dynamically invoking the code with those inputs. Even with random inputs, it is often capable of generating unexpected results such as crashes, memory corruption, or resource consumption. Fuzzing effectively produces repeatable test cases that clearly indicate bugs, which helps developers to diagnose the issues.

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-401 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-401?

This vulnerability occurs when a program allocates memory but fails to properly release it after it's no longer needed, causing a gradual accumulation of unused memory that can't be reclaimed by the system.

How serious is CWE-401?

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

What languages or platforms are affected by CWE-401?

MITRE lists the following affected platforms: C, C++.

How can I prevent CWE-401?

Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone. For example, glibc in Linux provides protection against free of invalid pointers. When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391]. To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and…

How does Plexicus detect and fix CWE-401?

Plexicus's SAST engine matches the data-flow signature for CWE-401 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-401?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/401.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-401

CWE-772 Parent

Missing Release of Resource after Effective Lifetime

This vulnerability occurs when a program fails to properly release a system resource—like memory, file handles, or network sockets—after…

CWE-1091 Sibling

Use of Object without Invoking Destructor Method

This weakness occurs when a program accesses an object but fails to properly call its destructor or finalizer method. This leaves the…

CWE-775 Sibling

Missing Release of File Descriptor or Handle after Effective Lifetime

This vulnerability occurs when a program fails to properly close file descriptors or handles after they are no longer needed, leaving…

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Further reading

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