Integer Coercion Error
Incomplete Variant
Structure: Simple
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.
Common Consequences 3
Scope: Availability
Impact: DoS: Resource Consumption (CPU)DoS: Resource Consumption (Memory)DoS: Crash, Exit, or Restart
Integer coercion often leads to undefined states of execution resulting in infinite loops or crashes.
Scope: IntegrityConfidentialityAvailability
Impact: Execute Unauthorized Code or Commands
In some cases, integer coercion errors can lead to exploitable buffer overflow conditions, resulting in the execution of arbitrary code.
Scope: IntegrityOther
Impact: Other
Integer coercion errors result in an incorrect value being stored for the variable in question.
Detection Methods 1
Automated Static AnalysisHigh
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.)Potential Mitigations 3
Phase: Requirements
A language which throws exceptions on ambiguous data casts might be chosen.
Phase: Architecture and Design
Design objects and program flow such that multiple or complex casts are unnecessary
Phase: Implementation
Ensure that any data type casting that you must used is entirely understood in order to reduce the plausibility of error in use.
Demonstrative Examples 2
ID : DX-21
The following code is intended to read an incoming packet from a socket and extract one or more headers.Code Example:
Bad
C
cThe 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 (Signed to Unsigned Conversion Error). 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.
ID : DX-23
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.Code Example:
Bad
C
cThis code first exhibits an example of Numeric Range Comparison Without Minimum Check, 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 (Improper Restriction of Operations within the Bounds of a Memory Buffer).
Observed Examples 1
CVE-2022-2639Chain: integer coercion error (Integer Coercion Error) prevents a return value from indicating an error, leading to out-of-bounds write (Out-of-bounds Write)
References 3
24 Deadly Sins of Software Security
Michael Howard, David LeBlanc, and John Viega
McGraw-Hill
2010
ID: REF-44
The Art of Software Security Assessment
Mark Dowd, John McDonald, and Justin Schuh
Addison Wesley
2006
ID: REF-62
The CLASP Application Security Process
Secure Software, Inc.
2005
ID: REF-18
Likelihood of Exploit
Medium
Applicable Platforms
Languages:
C : UndeterminedC++ : UndeterminedJava : UndeterminedC# : Undetermined
Modes of Introduction
Implementation
Related Weaknesses
Taxonomy Mapping
- CLASP
- CERT C Secure Coding
- CERT C Secure Coding
- CERT C Secure Coding
Notes
MaintenanceWithin C, it might be that "coercion" is semantically different than "casting", possibly depending on whether the programmer directly specifies the conversion, or if the compiler does it implicitly. This has implications for the presentation of this entry and others, such as Incorrect Conversion between Numeric Types, and whether there is enough of a difference for these entries to be split.