CWE-192: Integer Coercion Error

Description

Integer coercion refers to a set of flaws pertaining to the type casting, extension, or truncation of primitive data types.

Several flaws fall under the category of integer coercion errors. For the most part, these errors in and of themselves result only in availability and data integrity issues. However, in some circumstances, they may result in other, more complicated security related flaws, such as buffer overflow conditions.

Potential Impact

Availability

DoS: Resource Consumption (CPU), DoS: Resource Consumption (Memory), DoS: Crash, Exit, or Restart

Integrity, Confidentiality, Availability

Execute Unauthorized Code or Commands

Integrity, Other

Other

Demonstrative Examples

The following code is intended to read an incoming packet from a socket and extract one or more headers.

Bad

DataPacket *packet;int numHeaders;PacketHeader *headers;
                     sock=AcceptSocketConnection();ReadPacket(packet, sock);numHeaders =packet->headers;
                     if (numHeaders > 100) {ExitError("too many headers!");}headers = malloc(numHeaders * sizeof(PacketHeader);ParsePacketHeaders(packet, headers);

The code performs a check to make sure that the packet does not contain too many headers. However, numHeaders is defined as a signed int, so it could be negative. If the incoming packet specifies a value such as -3, then the malloc calculation will generate a negative number (say, -300 if each header can be a maximum of 100 bytes). When this result is provided to malloc(), it is first converted to a size_t type. This conversion then produces a large value such as 4294966996, which may cause malloc() to fail or to allocate an extremely large amount of memory (CWE-195). With the appropriate negative numbers, an attacker could trick malloc() into using a very small positive number, which then allocates a buffer that is much smaller than expected, potentially leading to a buffer overflow.

The following code reads a maximum size and performs validation on that size. It then performs a strncpy, assuming it will not exceed the boundaries of the array. While the use of "short s" is forced in this particular example, short int's are frequently used within real-world code, such as code that processes structured data.

Bad

int GetUntrustedInt () {return(0x0000FFFF);}
                     void main (int argc, char **argv) {
                        char path[256];char *input;int i;short s;unsigned int sz;
                           i = GetUntrustedInt();s = i;/* s is -1 so it passes the safety check - CWE-697 */if (s > 256) {DiePainfully("go away!\n");}
                           /* s is sign-extended and saved in sz */sz = s;
                           /* output: i=65535, s=-1, sz=4294967295 - your mileage may vary */printf("i=%d, s=%d, sz=%u\n", i, s, sz);
                           input = GetUserInput("Enter pathname:");
                           /* strncpy interprets s as unsigned int, so it's treated as MAX_INT(CWE-195), enabling buffer overflow (CWE-119) */strncpy(path, input, s);path[255] = '\0'; /* don't want CWE-170 */printf("Path is: %s\n", path);
                     }

This code first exhibits an example of CWE-839, allowing "s" to be a negative number. When the negative short "s" is converted to an unsigned integer, it becomes an extremely large positive integer. When this converted integer is used by strncpy() it will lead to a buffer overflow (CWE-119).

Mitigations & Prevention

Requirements

A language which throws exceptions on ambiguous data casts might be chosen.

Architecture and Design

Design objects and program flow such that multiple or complex casts are unnecessary

Implementation

Ensure that any data type casting that you must used is entirely understood in order to reduce the plausibility of error in use.

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 ID	Description
CVE-2022-2639	Chain: integer coercion error (CWE-192) prevents a return value from indicating an error, leading to out-of-bounds write (CWE-787)

Taxonomy Mappings

CLASP: — Integer coercion error
CERT C Secure Coding: INT02-C — Understand integer conversion rules
CERT C Secure Coding: INT05-C — Do not use input functions to convert character data if they cannot handle all possible inputs
CERT C Secure Coding: INT31-C — Ensure that integer conversions do not result in lost or misinterpreted data

Frequently Asked Questions

What is CWE-192?

CWE-192 (Integer Coercion Error) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. Integer coercion refers to a set of flaws pertaining to the type casting, extension, or truncation of primitive data types.

How can CWE-192 be exploited?

Attackers can exploit CWE-192 (Integer Coercion Error) to dos: resource consumption (cpu), dos: resource consumption (memory), dos: crash, exit, or restart. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-192?

Key mitigations include: A language which throws exceptions on ambiguous data casts might be chosen.

What is the severity of CWE-192?

CWE-192 is classified as a Variant-level weakness (Low-Medium abstraction). It has been observed in 1 real-world CVEs.