CWE-843: Access of Resource Using Incompatible Type… | Glexia
CWE-843 (Access of Resource Using Incompatible Type ('Type Confusion')) weakness overview with consequences, detection methods, mitigations, related CVEs and MITRE…
Glexia's Take · Automated analysis
CWE-843: Object Type Confusion
Access of Resource Using Incompatible Type ('Type Confusion') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Executive Impact
- Availability Integrity Confidentiality: Read Memory Modify Memory Execute Unauthorized Code or Commands DoS: Crash, Exit, or Restart: When a memory buffer is accessed using the wrong type, it could read or write memory out of the bounds of the buffer, if the allocated buffer is smaller than the type that the code is attempting to access, leading to a crash and possibly code execution.
Developer Pattern
CWE-843 is the kind of defect developers can usually prevent with explicit validation, safer framework defaults, and tests that exercise hostile input or unsafe state transitions.
Automation confidence
high confidence from CWE-843, 4.20.
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Official CWE Definition
CWE-843: Access of Resource Using Incompatible Type ('Type Confusion')
The product 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 product 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.
Developer And Remediation Guidance
How teams prevent and detect this weakness
Causes
- The following code uses a union to support the representation of different types of messages. It formats messages differently, depending on their type. The code intends to process the message as a NAME_TYPE, and sets the default message to "Hello World." However, since both buf.name 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 buf.name - a string. Execution of the program might generate output such as: Pointer of name is 10830 Pointer of name is now 10831 Message: ello World Notice how the pointer for buf.name was changed, even though buf.name 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 buf.name 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. When called with the following query string: value=123 the program calculates the sum and prints out: SUM is 128 However, the attacker could supply a query string such as: value[]=123 The "[]" array syntax causes $value to be treated as an array type, which then generates a fatal error when calculating $sum: Fatal error: Unsupported operand types in program.php on line 2
- 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 $UserPrivilegeArray reference. It is expected that only userID 3 is an admin (since this is listed in the third element of the array). In this case, the programmer intended to use "$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.
Remediation
- Use safe APIs
- Centralize the control
- Add regression tests
- Review logs and telemetry for attempted abuse
Detection
- Automated Static Analysis: 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.)
Mappings
Related CVEs, CWEs, and ATT&CK context
Related CWEs
No related CWE relationships are published yet.
ATT&CK Relevance
ATT&CK relevance is shown only when reviewed or responsibly inferred.