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cwe:cn:definition:190

CWE-190:整数溢出或超界折返

Description Summary

The software performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control.

Extended Description

An integer overflow or wraparound occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may wrap to become a very small or negative number. While this may be intended behavior in circumstances that rely on wrapping, it can have security consequences if the wrap is unexpected. This is especially the case if the integer overflow can be triggered using user-supplied inputs. This becomes security-critical when the result is used to control looping, make a security decision, or determine the offset or size in behaviors such as memory allocation, copying, concatenation, etc.

Likelihood of Exploit

Medium

Common Consequences

Scope Technical Impace Note
AvailabilityDoS: crash / exit / restart
DoS: resource consumption (CPU)
DoS: resource consumption (memory)
DoS: instability
This weakness will generally lead to undefined behavior and therefore crashes. In the case of overflows involving loop index variables, the likelihood of infinite loops is also high.
IntegrityModify memoryIf the value in question is important to data (as opposed to flow), simple data corruption has occurred. Also, if the wrap around results in other conditions such as buffer overflows, further memory corruption may occur.
Confidentiality
Availability
Access_Control
Execute unauthorized code or commands
Bypass protection mechanism
This weakness can sometimes trigger buffer overflows which can be used to execute arbitrary code. This is usually outside the scope of a program's implicit security policy.

Detection Methods

Detection Method - 1

Automated Static Analysis

This weakness can often be detected using automated static analysis tools. Many modern tools use data flow analysis or constraint-based techniques to minimize the number of false positives.

Automated static analysis might not be able to recognize when proper input validation is being performed, leading to false positives - i.e., warnings that do not have any security consequences or do not require any code changes.

Automated static analysis might not be able to detect the usage of custom API functions or third-party libraries that indirectly invoke SQL commands, leading to false negatives - especially if the API/library code is not available for analysis.

This is not a perfect solution, since 100% accuracy and coverage are not feasible.
2013/05/30 09:36

Detection Method - 2

Automated Dynamic Analysis

This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

2013/05/30 09:36

Detection Method - 3

Manual Analysis

This weakness can be detected using tools and techniques that require manual (human) analysis, such as penetration testing, threat modeling, and interactive tools that allow the tester to record and modify an active session.

Specifically, manual analysis can be useful for finding this weakness, and for minimizing false positives assuming an understanding of business logic. However, it might not achieve desired code coverage within limited time constraints. For black-box analysis, if credentials are not known for privileged accounts, then the most security-critical portions of the application may not receive sufficient attention.

Consider using OWASP CSRFTester to identify potential issues and aid in manual analysis.

These may be more effective than strictly automated techniques. This is especially the case with weaknesses that are related to design and business rules.
2013/05/30 09:37

Detection Method - 4

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Detection Method - 5

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Detection Method - 6

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Detection Method - 7

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Detection Method - 8

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Potential Mitigations

Mitigation - 1

Requirements

Ensure that all protocols are strictly defined, such that all out-of-bounds behavior can be identified simply, and require strict conformance to the protocol.

Mitigation - 2

Requirements

Strategy:Language Selection

Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.

Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.

2013/05/30 09:37

Mitigation - 3

Architecture and Design

Strategy:Libraries or Frameworks

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

For example, use anti-CSRF packages such as the OWASP CSRFGuard. [R.352.3]

Another example is the ESAPI Session Management control, which includes a component for CSRF. [R.352.9]

2013/05/30 09:36

Mitigation - 4

Implementation

Strategy:Input Validation

Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.

2013/05/30 09:37

Mitigation - 5

Implementation

Understand the programming language's underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, “not-a-number” calculations, and how the language handles numbers that are too large or too small for its underlying representation. [R.190.3]

Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.

2013/05/30 13:23

Mitigation - 6

Architecture and Design

For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

2013/05/30 09:37

Mitigation - 7

Implementation

Strategy:Compilation or Build Hardening

Examine compiler warnings closely and eliminate problems with potential security implications, such as signed / unsigned mismatch in memory operations, or use of uninitialized variables. Even if the weakness is rarely exploitable, a single failure may lead to the compromise of the entire system.

2013/05/30 09:37

Demonstrative Examples

Example - 1

The following image processing code allocates a table for images.

img_t table_ptr; /*struct containing img data, 10kB each*/ 
int num_imgs; 
... 
num_imgs = get_num_imgs(); 
table_ptr = (img_t*)malloc(sizeof(img_t)*num_imgs); 
... 

This code intends to allocate a table of size num_imgs, however as num_imgs grows large, the calculation determining the size of the list will eventually overflow (CWE-190). This will result in a very small list to be allocated instead. If the subsequent code operates on the list as if it were num_imgs long, it may result in many types of out-of-bounds problems (CWE-119).

2013/05/30 13:23

Example - 2

The following code excerpt from OpenSSH 3.3 demonstrates a classic case of integer overflow:

nresp = packet_get_int(); 
if (nresp > 0) { 
response = xmalloc(nresp*sizeof(char*)); 
for (i = 0; i < nresp; i++) response[i] = packet_get_string(NULL); 
 
} 

If nresp has the value 1073741824 and sizeof(char*) has its typical value of 4, then the result of the operation nresp*sizeof(char*) overflows, and the argument to xmalloc() will be 0. Most malloc() implementations will happily allocate a 0-byte buffer, causing the subsequent loop iterations to overflow the heap buffer response.

Example - 3

Integer overflows can be complicated and difficult to detect. The following example is an attempt to show how an integer overflow may lead to undefined looping behavior:

short int bytesRec = 0; 
char buf[SOMEBIGNUM]; 
 
while(bytesRec < MAXGET) { 
bytesRec += getFromInput(buf+bytesRec); 
 
} 

In the above case, it is entirely possible that bytesRec may overflow, continuously creating a lower number than MAXGET and also overwriting the first MAXGET-1 bytes of buf.

Example - 4

In this example the method determineFirstQuarterRevenue is used to determine the first quarter revenue for an accounting/business application. The method retrieves the monthly sales totals for the first three months of the year, calculates the first quarter sales totals from the monthly sales totals, calculates the first quarter revenue based on the first quarter sales, and finally saves the first quarter revenue results to the database.

#define JAN 1 
#define FEB 2 
#define MAR 3 
 
short getMonthlySales(int month) {...} 
 
float calculateRevenueForQuarter(short quarterSold) {...} 
 
int determineFirstQuarterRevenue() { 
 
// Variable for sales revenue for the quarter 
float quarterRevenue = 0.0f; 
 
short JanSold = getMonthlySales(JAN); /* Get sales in January */ 
short FebSold = getMonthlySales(FEB); /* Get sales in February */ 
short MarSold = getMonthlySales(MAR); /* Get sales in March */ 
 
// Calculate quarterly total 
short quarterSold = JanSold + FebSold + MarSold; 
 
// Calculate the total revenue for the quarter 
quarterRevenue = calculateRevenueForQuarter(quarterSold); 
 
saveFirstQuarterRevenue(quarterRevenue); 
 
return 0; 
 
} 

However, in this example the primitive type short int is used for both the monthly and the quarterly sales variables. In C the short int primitive type has a maximum value of 32768. This creates a potential integer overflow if the value for the three monthly sales adds up to more than the maximum value for the short int primitive type. An integer overflow can lead to data corruption, unexpected behavior, infinite loops and system crashes. To correct the situation the appropriate primitive type should be used, as in the example below, and/or provide some validation mechanism to ensure that the maximum value for the primitive type is not exceeded.

... 
float calculateRevenueForQuarter(long quarterSold) {...} 
 
int determineFirstQuarterRevenue() { 
... 
// Calculate quarterly total 
long quarterSold = JanSold + FebSold + MarSold; 
 
// Calculate the total revenue for the quarter 
quarterRevenue = calculateRevenueForQuarter(quarterSold); 
 
... 
 
} 

Note that an integer overflow could also occur if the quarterSold variable has a primitive type long but the method calculateRevenueForQuarter has a parameter of type short.

Observed Examples

Reference Description
CVE-2010-2753chain: integer overflow leads to use-after-free
CVE-2002-0391Integer overflow via a large number of arguments.
CVE-2002-0639Integer overflow in OpenSSH as listed in the demonstrative examples.
CVE-2005-1141Image with large width and height leads to integer overflow.
CVE-2005-0102Length value of -1 leads to allocation of 0 bytes and resultant heap overflow.
CVE-2004-2013Length value of -1 leads to allocation of 0 bytes and resultant heap overflow.
cwe/cn/definition/190.txt · 最后更改: 2014/09/04 14:27 (外部编辑)