CWE-843 使用不兼容类型访问资源(类型混淆)

Access of Resource Using Incompatible Type ('Type Confusion')

结构: Simple

Abstraction: Base

状态: Incomplete

被利用可能性: unkown


The program allocates or initializes a resource such as a pointer, object, or variable using one type, but it later accesses that resource using a type that is incompatible with the original type.


When the program accesses the resource using an incompatible type, this could trigger logical errors because the resource does not have expected properties. In languages without memory safety, such as C and C++, type confusion can lead to out-of-bounds memory access.

While this weakness is frequently associated with unions when parsing data with many different embedded object types in C, it can be present in any application that can interpret the same variable or memory location in multiple ways.

This weakness is not unique to C and C++. For example, errors in PHP applications can be triggered by providing array parameters when scalars are expected, or vice versa. Languages such as Perl, which perform automatic conversion of a variable of one type when it is accessed as if it were another type, can also contain these issues.


  • cwe_Nature: ChildOf cwe_CWE_ID: 704 cwe_View_ID: 1000 cwe_Ordinal: Primary

  • cwe_Nature: ChildOf cwe_CWE_ID: 704 cwe_View_ID: 1003 cwe_Ordinal: Primary

  • cwe_Nature: ChildOf cwe_CWE_ID: 704 cwe_View_ID: 699 cwe_Ordinal: Primary

  • cwe_Nature: CanPrecede cwe_CWE_ID: 119 cwe_View_ID: 1000


Language: [{'cwe_Name': 'C', 'cwe_Prevalence': 'Undetermined'}, {'cwe_Name': 'C++', 'cwe_Prevalence': 'Undetermined'}]


The following code uses a union to support the representation of different types of messages. It formats messages differently, depending on their type.

bad C

#define NAME_TYPE 1
#define ID_TYPE 2

struct MessageBuffer
int msgType;
union {
char name;
int nameID;

int main (int argc, char
argv) {
struct MessageBuffer buf;
defaultMessage = "Hello World";

buf.msgType = NAME_TYPE; = defaultMessage;
printf("Pointer of is %p\n",;
/ This particular value for nameID is used to make the code architecture-independent. If coming from untrusted input, it could be any value. /

buf.nameID = (int)(defaultMessage + 1);
printf("Pointer of is now %p\n",;
if (buf.msgType == NAME_TYPE) {
printf("Message: %s\n",;
else {
printf("Message: Use ID %d\n", buf.nameID);

The code intends to process the message as a NAME_TYPE, and sets the default message to "Hello World." However, since both and buf.nameID are part of the same union, they can act as aliases for the same memory location, depending on memory layout after compilation.

As a result, modification of buf.nameID - an int - can effectively modify the pointer that is stored in - a string.

Execution of the program might generate output such as:


Notice how the pointer for was changed, even though was not explicitly modified.

In this case, the first "H" character of the message is omitted. However, if an attacker is able to fully control the value of buf.nameID, then could contain an arbitrary pointer, leading to out-of-bounds reads or writes.

The following PHP code accepts a value, adds 5, and prints the sum.

bad PHP

$value = $_GET['value'];
$sum = $value + 5;
echo "value parameter is '$value'<p>";
echo "SUM is $sum";

When called with the following query string:


the program calculates the sum and prints out:


However, the attacker could supply a query string such as:


The "[]" array syntax causes $value to be treated as an array type, which then generates a fatal error when calculating $sum:


The following Perl code is intended to look up the privileges for user ID's between 0 and 3, by performing an access of the $UserPrivilegeArray reference. It is expected that only userID 3 is an admin (since this is listed in the third element of the array).

bad Perl

my $UserPrivilegeArray = ["user", "user", "admin", "user"];

my $userID = get_current_user_ID();

if ($UserPrivilegeArray eq "user") {
print "Regular user!\n";
else {
print "Admin!\n";

print "\$UserPrivilegeArray = $UserPrivilegeArray\n";

In this case, the programmer intended to use "$UserPrivilegeArray->{$userID}" to access the proper position in the array. But because the subscript was omitted, the "user" string was compared to the scalar representation of the $UserPrivilegeArray reference, which might be of the form "ARRAY(0x229e8)" or similar.

Since the logic also "fails open" (CWE-636), the result of this bug is that all users are assigned administrator privileges.

While this is a forced example, it demonstrates how type confusion can have security consequences, even in memory-safe languages.


标识 说明 链接
CVE-2010-4577 Type confusion in CSS sequence leads to out-of-bounds read.
CVE-2011-0611 Size inconsistency allows code execution, first discovered when it was actively exploited in-the-wild.
CVE-2010-0258 Improperly-parsed file containing records of different types leads to code execution when a memory location is interpreted as a different object than intended.


Applicable Platform

Research Gap


映射的分类名 ImNode ID Fit Mapped Node Name
CERT C Secure Coding EXP39-C Exact Do not access a variable through a pointer of an incompatible type