CWE-416 Variant Stable High likelihood

Use After Free

Use After Free happens when a program continues to use a pointer to a memory location after that memory has been freed. This can lead to unpredictable behavior, crashes, or security vulnerabilities…

Definition

What is CWE-416?

Use After Free happens when a program continues to use a pointer to a memory location after that memory has been freed. This can lead to unpredictable behavior, crashes, or security vulnerabilities because the freed memory may have been reallocated for a different purpose.
This vulnerability occurs because the pointer isn't invalidated after `free()` is called. The memory manager can then reassign that same memory block to a different part of the program, perhaps for storing unrelated data. When the original, now 'dangling' pointer is used again, it reads or writes to this new data, corrupting it and leading to instability or exploitable conditions like arbitrary code execution. Detecting use-after-free bugs manually is challenging as they often depend on complex, state-specific execution paths. While SAST tools can flag the dangerous pattern, Plexicus uses AI to analyze context and suggest precise code fixes—such as nullifying pointers or reordering logic—saving developers hours of manual debugging and helping secure the entire application lifecycle.
Vulnerability Diagram CWE-416
Use After Free malloc → p free(p) p still held attacker malloc reclaims slot use *p (vtable call) jumps to attacker data A freed pointer is reused after the slot is owned by attacker data.
Real-world impact

Real-world CVEs caused by CWE-416

  • CVE-2022-20141

    Chain: an operating system kernel has insufficent resource locking (CWE-413) leading to a use after free (CWE-416).

  • CVE-2022-2621

    Chain: two threads in a web browser use the same resource (CWE-366), but one of those threads can destroy the resource before the other has completed (CWE-416).

  • CVE-2021-0920

    Chain: mobile platform race condition (CWE-362) leading to use-after-free (CWE-416), as exploited in the wild per CISA KEV.

  • CVE-2020-6819

    Chain: race condition (CWE-362) leads to use-after-free (CWE-416), as exploited in the wild per CISA KEV.

  • CVE-2010-4168

    Use-after-free triggered by closing a connection while data is still being transmitted.

  • CVE-2010-2941

    Improper allocation for invalid data leads to use-after-free.

  • CVE-2010-2547

    certificate with a large number of Subject Alternate Names not properly handled in realloc, leading to use-after-free

  • CVE-2010-1772

    Timers are not disabled when a related object is deleted

How attackers exploit it

Step-by-step attacker path

  1. 1

    The following example demonstrates the weakness.

  2. 2

    The following code illustrates a use after free error:

  3. 3

    When an error occurs, the pointer is immediately freed. However, this pointer is later incorrectly used in the logError function.

Vulnerable code example

Vulnerable C

The following example demonstrates the weakness.

Vulnerable C 
#include <stdio.h>
  #include <unistd.h>
  #define BUFSIZER1 512
  #define BUFSIZER2 ((BUFSIZER1/2) - 8)
  int main(int argc, char **argv) {
  	char *buf1R1;
  	char *buf2R1;
  	char *buf2R2;
  	char *buf3R2;
  	buf1R1 = (char *) malloc(BUFSIZER1);
  	buf2R1 = (char *) malloc(BUFSIZER1);
  	free(buf2R1);
  	buf2R2 = (char *) malloc(BUFSIZER2);
  	buf3R2 = (char *) malloc(BUFSIZER2);
  	strncpy(buf2R1, argv[1], BUFSIZER1-1);
  	free(buf1R1);
  	free(buf2R2);
  	free(buf3R2);
  }
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-416

  • Architecture and Design Choose a language that provides automatic memory management.
  • Implementation When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Detection signals

How to detect CWE-416

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-416 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-416?

Use After Free happens when a program continues to use a pointer to a memory location after that memory has been freed. This can lead to unpredictable behavior, crashes, or security vulnerabilities because the freed memory may have been reallocated for a different purpose.

How serious is CWE-416?

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-416?

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

How can I prevent CWE-416?

Choose a language that provides automatic memory management. When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.

How does Plexicus detect and fix CWE-416?

Plexicus's SAST engine matches the data-flow signature for CWE-416 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-416?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/416.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-416

CWE-825 Parent

Expired Pointer Dereference

This vulnerability occurs when a program tries to use a pointer that still points to a memory location that has already been freed or…

CWE-415 Sibling

Double Free

A double free vulnerability occurs when a program mistakenly calls the 'free()' function twice on the same block of memory.

CWE-120 Can precede

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

This vulnerability occurs when a program copies data from one memory location to another without first verifying that the source data will…

CWE-123 Can precede

Write-what-where Condition

A write-what-where condition occurs when an attacker can control both the data written and the exact memory location where it's written,…

Resources

Further reading

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