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Base · Medium

CWE-908: Use of Uninitialized Resource

The product uses or accesses a resource that has not been initialized.

CWE-908 · Base Level ·13 CVEs ·4 Mitigations

Description

The product uses or accesses a resource that has not been initialized.

When a resource has not been properly initialized, the product may behave unexpectedly. This may lead to a crash or invalid memory access, but the consequences vary depending on the type of resource and how it is used within the product.

Potential Impact

Confidentiality

Read Memory, Read Application Data

Availability

DoS: Crash, Exit, or Restart

Demonstrative Examples

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.
Bad
private boolean initialized = true;public void someMethod() {
                        if (!initialized) {
                              
                                 
                                 // perform initialization tasks
                                 ...
                                 initialized = true;
                           }
The following code intends to limit certain operations to the administrator only.
Bad
$username = GetCurrentUser();$state = GetStateData($username);if (defined($state)) {$uid = ExtractUserID($state);}
                     
                     # do stuff
                     if ($uid == 0) {DoAdminThings();}
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.
The following code intends to concatenate a string to a variable and print the string.
Bad
char str[20];strcat(str, "hello world");printf("%s", str);
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 CWE-14 or CWE-244). 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 (CWE-126) if a null terminator isn't found before the end of the memory segment is reached, leading to a segmentation fault and crash.
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 (CWE-456). 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.
Bad
char *test_string;
                if (i != err_val)
                {
                test_string = "Hello World!";
                }
                printf("%s", test_string);
Good
char *test_string = "Done at the beginning";
				if (i != err_val)
				{
				test_string = "Hello World!";
				}
				printf("%s", test_string);
Another solution is to ensure that each branch of the conditional - including the default/else branch - could ensure that test_string is set:
Good
char *test_string;
				if (i != err_val)
				{
				test_string = "Hello World!";
				}
				else {
				test_string = "Done on the other side!";
				}
				printf("%s", test_string);

Mitigations & Prevention

Implementation

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

Implementation

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

Implementation

Avoid race conditions (CWE-362) during initialization routines.

Build and Compilation

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

Detection Methods

  • 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 sea

Real-World CVE Examples

CVE IDDescription
CVE-2019-9805Chain: Creation of the packet client occurs before initialization is complete (CWE-696) resulting in a read from uninitialized memory (CWE-908), 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 (CWE-862) of a user results from an improperly initialized (CWE-909) 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: Use of an unimplemented network socket operation pointing to an uninitialized handler function (CWE-456) causes a crash because of a null pointer dereference (CWE-476)
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

CWE-665: Improper Initialization

The product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected s...

Taxonomy Mappings

  • CERT C Secure Coding: EXP33-C — Do not read uninitialized memory

Frequently Asked Questions

What is CWE-908?

CWE-908 (Use of Uninitialized Resource) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. The product uses or accesses a resource that has not been initialized.

How can CWE-908 be exploited?

Attackers can exploit CWE-908 (Use of Uninitialized Resource) to read memory, read application data. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-908?

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

What is the severity of CWE-908?

CWE-908 is classified as a Base-level weakness (Medium abstraction). It has been observed in 13 real-world CVEs.