Use of Uninitialized Resource

Incomplete Base

Structure: Simple

Description

This vulnerability occurs when software attempts to use a resource—like memory, a file handle, or an object—before it has been properly set up or assigned a valid starting state.

Extended Description

Using an uninitialized resource is like trying to drive a car without starting the engine; the system doesn't have a valid state to operate from. This often happens due to coding oversights, such as forgetting to assign a value to a variable, failing to open a file before reading it, or not constructing an object before calling its methods. The specific resource could be anything from a block of memory and a database connection to a configuration setting or a network socket. The consequences depend entirely on what the resource is and how the program tries to use it. At best, the software might behave unpredictably or produce incorrect results. More severely, it can crash the application, expose sensitive data leftover in memory, or create a path for attackers to manipulate the program's control flow. This makes it a common root cause for stability issues and a potential gateway to more serious security exploits.

Common Consequences 2

Scope: Confidentiality

Impact: Read MemoryRead Application Data

When reusing a resource such as memory or a program variable, the original contents of that resource may not be cleared before it is sent to an untrusted party.

Scope: Availability

Impact: DoS: Crash, Exit, or Restart

The uninitialized resource may contain values that cause program flow to change in ways that the programmer did not intend.

Potential Mitigations 4

Phase: Implementation

Explicitly initialize the resource before use. If this is performed through an API function or standard procedure, follow all required steps.

Phase: Implementation

Pay close attention to complex conditionals that affect initialization, since some branches might not perform the initialization.

Phase: Implementation

Avoid race conditions (Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')) during initialization routines.

Phase: Build and Compilation

Run or compile the product with settings that generate warnings about uninitialized variables or data.

Demonstrative Examples 4

ID : DX-105

Here, a boolean initiailized field is consulted to ensure that initialization tasks are only completed once. However, the field is mistakenly set to true during static initialization, so the initialization code is never reached.

Code Example:

Bad

Java

java

// perform initialization tasks* ...

java

ID : DX-54

The following code intends to limit certain operations to the administrator only.

Code Example:Bad
Perl
perldo stuff*perl

If the application is unable to extract the state information - say, due to a database timeout - then the $uid variable will not be explicitly set by the programmer. This will cause $uid to be regarded as equivalent to "0" in the conditional, allowing the original user to perform administrator actions. Even if the attacker cannot directly influence the state data, unexpected errors could cause incorrect privileges to be assigned to a user just by accident.

ID : DX-106

The following code intends to concatenate a string to a variable and print the string.

Code Example:Bad
C
c

This might seem innocent enough, but str was not initialized, so it contains random memory. As a result, str[0] might not contain the null terminator, so the copy might start at an offset other than 0. The consequences can vary, depending on the underlying memory.

If a null terminator is found before str[8], then some bytes of random garbage will be printed before the "hello world" string. The memory might contain sensitive information from previous uses, such as a password (which might occur as a result of Compiler Removal of Code to Clear Buffers or Improper Clearing of Heap Memory Before Release ('Heap Inspection')). In this example, it might not be a big deal, but consider what could happen if large amounts of memory are printed out before the null terminator is found.

If a null terminator isn't found before str[8], then a buffer overflow could occur, since strcat will first look for the null terminator, then copy 12 bytes starting with that location. Alternately, a buffer over-read might occur (Buffer Over-read) if a null terminator isn't found before the end of the memory segment is reached, leading to a segmentation fault and crash.

ID : DX-144

This example will leave test_string in an unknown condition when i is the same value as err_val, because test_string is not initialized (Missing Initialization of a Variable). Depending on where this code segment appears (e.g. within a function body), test_string might be random if it is stored on the heap or stack. If the variable is declared in static memory, it might be zero or NULL. Compiler optimization might contribute to the unpredictability of this address.

Code Example:

Bad

char *test_string; if (i != err_val) {

When the printf() is reached, test_string might be an unexpected address, so the printf might print junk strings (Use of Uninitialized Variable). To fix this code, there are a couple approaches to making sure that test_string has been properly set once it reaches the printf(). One solution would be to set test_string to an acceptable default before the conditional:

Code Example:

Good

char *test_string = "Done at the beginning"; if (i != err_val) {

Another solution is to ensure that each branch of the conditional - including the default/else branch - could ensure that test_string is set:

Code Example:

Good

char *test_string; if (i != err_val) {

Observed Examples 13

CVE-2019-9805Chain: Creation of the packet client occurs before initialization is complete (Incorrect Behavior Order) resulting in a read from uninitialized memory (Use of Uninitialized Resource), causing memory corruption.

CVE-2008-4197Use of uninitialized memory may allow code execution.

CVE-2008-2934Free of an uninitialized pointer leads to crash and possible code execution.

CVE-2008-0063Product does not clear memory contents when generating an error message, leading to information leak.

CVE-2008-0062Lack of initialization triggers NULL pointer dereference or double-free.

CVE-2008-0081Uninitialized variable leads to code execution in popular desktop application.

CVE-2008-3688Chain: Uninitialized variable leads to infinite loop.

CVE-2008-3475Chain: Improper initialization leads to memory corruption.

CVE-2005-1036Chain: Bypass of access restrictions due to improper authorization (Missing Authorization) of a user results from an improperly initialized (Missing Initialization of Resource) I/O permission bitmap

CVE-2008-3597Chain: game server can access player data structures before initialization has happened leading to NULL dereference

CVE-2009-2692Chain: uninitialized function pointers can be dereferenced allowing code execution

CVE-2009-0949Chain: improper initialization of memory can lead to NULL dereference

CVE-2009-3620Chain: some unprivileged ioctls do not verify that a structure has been initialized before invocation, leading to NULL dereference

References 1

Exploiting Uninitialized Data

mercy

01-2006

https://web.archive.org/web/20070403193636/http://www.felinemenace.org/~mercy/papers/UBehavior/UBehavior.zip(2025-07-24)

ID: REF-436

Likelihood of Exploit

Medium

Applicable Platforms

Languages:

Not Language-Specific : Undetermined

Modes of Introduction

Implementation

Related Weaknesses

ChildOf:

Improper Initialization (CWE-665)

ChildOf:

Improper Initialization (CWE-665)

Taxonomy Mapping

CERT C Secure Coding