Vulnerability Mapping:ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities Abstraction:
VariantVariant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.
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Description
Integer coercion refers to a set of flaws pertaining to the type casting, extension, or truncation of primitive data types.
Extended Description
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
This table specifies different individual consequences
associated with the weakness. The Scope identifies the application security area that is
violated, while the Impact describes the negative technical impact that arises if an
adversary succeeds in exploiting this weakness. The Likelihood provides information about
how likely the specific consequence is expected to be seen relative to the other
consequences in the list. For example, there may be high likelihood that a weakness will be
exploited to achieve a certain impact, but a low likelihood that it will be exploited to
achieve a different impact.
Integer coercion often leads to undefined states of execution resulting in infinite loops or crashes.
Integrity Confidentiality Availability
Technical 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.
Integrity Other
Technical Impact: Other
Integer coercion errors result in an incorrect value being stored for the variable in question.
Potential Mitigations
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.
Relationships
This table shows the weaknesses and high level categories that are related to this
weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to
similar items that may exist at higher and lower levels of abstraction. In addition,
relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user
may want to explore.
Relevant to the view "Research Concepts" (CWE-1000)
Nature
Type
ID
Name
ChildOf
Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
The different Modes of Introduction provide information
about how and when this
weakness may be introduced. The Phase identifies a point in the life cycle at which
introduction
may occur, while the Note provides a typical scenario related to introduction during the
given
phase.
Phase
Note
Implementation
Applicable Platforms
This listing shows possible areas for which the given
weakness could appear. These
may be for specific named Languages, Operating Systems, Architectures, Paradigms,
Technologies,
or a class of such platforms. The platform is listed along with how frequently the given
weakness appears for that instance.
Languages
C
(Undetermined Prevalence)
C++
(Undetermined Prevalence)
Java
(Undetermined Prevalence)
C#
(Undetermined Prevalence)
Likelihood Of Exploit
Medium
Demonstrative Examples
Example 1
The following code is intended to read an incoming packet from a socket and extract one or more headers.
(bad code)
Example Language: C
DataPacket *packet; int numHeaders; PacketHeader *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.
Example 2
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 code)
Example Language: C
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).
Chain: integer coercion error (CWE-192) prevents a return value from indicating an error, leading to out-of-bounds write (CWE-787)
Detection
Methods
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.)
Effectiveness: High
Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that
reference this weakness as a member. This information is often useful in understanding where a
weakness fits within the context of external information sources.
Nature
Type
ID
Name
MemberOf
Category - a CWE entry that contains a set of other entries that share a common characteristic.
(this CWE ID may be used to map to real-world vulnerabilities)
Reason:
Acceptable-Use
Rationale:
This CWE entry is at the Variant level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comments:
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.
Notes
Maintenance
Within 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 CWE-681, and whether there is enough of a difference for these entries to be split.
Taxonomy
Mappings
Mapped Taxonomy Name
Node ID
Fit
Mapped Node Name
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
Exact
Ensure that integer conversions do not result in lost or misinterpreted data
References
[REF-44] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 7: Integer Overflows." Page 119. McGraw-Hill. 2010.
[REF-62] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 6, "Sign Extension", Page 248. 1st Edition. Addison Wesley. 2006.
Description
This table specifies different individual consequences
associated with the weakness. The Scope identifies the application security area that is
violated, while the Impact describes the negative technical impact that arises if an
adversary succeeds in exploiting this weakness. The Likelihood provides information about
how likely the specific consequence is expected to be seen relative to the other
consequences in the list. For example, there may be high likelihood that a weakness will be
exploited to achieve a certain impact, but a low likelihood that it will be exploited to
achieve a different impact.
