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cwe:cn:definition:119

CWE-119:内存缓冲区边界内操作的限制不恰当

Description Summary

The software performs operations on a memory buffer, but it can read from or write to a memory location that is outside of the intended boundary of the buffer.

Extended Description

Certain languages allow direct addressing of memory locations and do not automatically ensure that these locations are valid for the memory buffer that is being referenced. This can cause read or write operations to be performed on memory locations that may be associated with other variables, data structures, or internal program data.

As a result, an attacker may be able to execute arbitrary code, alter the intended control flow, read sensitive information, or cause the system to crash.

Likelihood of Exploit

High

Common Consequences

Scope Technical Impace Note
Integrity
Confidentiality
Availability
Execute unauthorized code or commands
Modify memory
If the memory accessible by the attacker can be effectively controlled, it may be possible to execute arbitrary code, as with a standard buffer overflow. If the attacker can overwrite a pointer's worth of memory (usually 32 or 64 bits), he can redirect a function pointer to his own malicious code. Even when the attacker can only modify a single byte arbitrary code execution can be possible. Sometimes this is because the same problem can be exploited repeatedly to the same effect. Other times it is because the attacker can overwrite security-critical application-specific data – such as a flag indicating whether the user is an administrator.
Availability
Confidentiality
Read memory
DoS: crash / exit / restart
DoS: resource consumption (CPU)
DoS: resource consumption (memory)
Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.
ConfidentialityRead memoryIn the case of an out-of-bounds read, the attacker may have access to sensitive information. If the sensitive information contains system details, such as the current buffers position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.

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

Automated Static Analysis - Binary / Bytecode

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

Detection Method - 4

Manual Static Analysis - Binary / Bytecode

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

Detection Method - 5

=== Dynamic Analysis with automated results interpretation === According to SOAR, the following detection techniques may be useful:

Detection Method - 6

Dynamic Analysis with manual results interpretation

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

Detection Method - 7

Manual Static Analysis - Source Code

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

Detection Method - 8

Automated Static Analysis - Source Code

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

Detection Method - 9

Architecture / Design Review

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

Potential Mitigations

Mitigation - 1

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 - 2

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.

Examples include the Safe C String Library (SafeStr) by Messier and Viega [R.805.6], and the Strsafe.h library from Microsoft [R.805.7]. These libraries provide safer versions of overflow-prone string-handling functions.

2013/05/30 09:37

Mitigation - 3

Build and Compilation

Strategy:Compilation or Build Hardening

Run or compile the software using features or extensions that automatically provide a protection mechanism that mitigates or eliminates buffer overflows.

For example, certain compilers and extensions provide automatic buffer overflow detection mechanisms that are built into the compiled code. Examples include the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice.

2013/05/30 09:37

Mitigation - 4

Implementation

Consider adhering to the following rules when allocating and managing an application's memory:

2013/05/30 09:37

Mitigation - 5

Operation

Strategy:Environment Hardening

Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.

Examples include Address Space Layout Randomization (ASLR) [R.806.3] [R.806.5] and Position-Independent Executables (PIE) [R.806.7].

2013/05/30 09:37

Mitigation - 6

Operation

Strategy:Environment Hardening

Use a CPU and operating system that offers Data Execution Protection (NX) or its equivalent [R.806.5] [R.806.6].

2013/05/30 09:37

Mitigation - 7

Implementation

Replace unbounded copy functions with analogous functions that support length arguments, such as strcpy with strncpy. Create these if they are not available.

2013/05/30 09:37

Demonstrative Examples

Example - 1

This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer.

void host_lookup(char *user_supplied_addr){ 
struct hostent *hp; 
in_addr_t *addr; 
char hostname[64]; 
in_addr_t inet_addr(const char *cp); 
 
/*routine that ensures user_supplied_addr is in the right format for conversion */ 
validate_addr_form(user_supplied_addr); 
addr = inet_addr(user_supplied_addr); 
hp = gethostbyaddr( addr, sizeof(struct in_addr), AF_INET); 
strcpy(hostname, hp->h_name); 
 
} 

If an attacker provides an address that appears to be well-formed, but the address does not resolve to a hostname, then the call to gethostbyaddr() will return NULL. Since the code does not check the return value from gethostbyaddr (CWE-252), a NULL pointer dereference (CWE-476) would then occur in the call to strcpy().

Note that this example is also vulnerable to a buffer overflow (see CWE-119).

2013/05/30 09:37

Example - 2

This example applies an encoding procedure to an input string and stores it into a buffer.

char * copy_input(char *user_supplied_string){ 
int i, dst_index; 
char *dst_buf = (char*)malloc(4*sizeof(char) * MAX_SIZE); 
if ( MAX_SIZE <= strlen(user_supplied_string) ){ 
die("user string too long, die evil hacker!"); 
 
} 
dst_index = 0; 
for ( i = 0; i < strlen(user_supplied_string); i++ ){ 
if( '&' == user_supplied_string[i] ){ 
dst_buf[dst_index++] = '&'; 
dst_buf[dst_index++] = 'a'; 
dst_buf[dst_index++] = 'm'; 
dst_buf[dst_index++] = 'p'; 
dst_buf[dst_index++] = ';'; 
 
} 
else if ('<' == user_supplied_string[i] ){ 
/* encode to &lt; */ 
 
} 
else dst_buf[dst_index++] = user_supplied_string[i]; 
 
} 
return dst_buf; 
 
} 

The programmer attempts to encode the ampersand character in the user-controlled string, however the length of the string is validated before the encoding procedure is applied. Furthermore, the programmer assumes encoding expansion will only expand a given character by a factor of 4, while the encoding of the ampersand expands by 5. As a result, when the encoding procedure expands the string it is possible to overflow the destination buffer if the attacker provides a string of many ampersands.

2013/05/30 13:23

Example - 3

The following example asks a user for an offset into an array to select an item.

int main (int argc, char **argv) { 
char *items[] = {"boat", "car", "truck", "train"}; 
int index = GetUntrustedOffset(); 
printf("You selected %s\n", items[index-1]); 
 
} 

The programmer allows the user to specify which element in the list to select, however an attacker can provide an out-of-bounds offset, resulting in a buffer over-read (CWE-126).

2013/05/30 13:23

Example - 4

In the following code, the method retrieves a value from an array at a specific array index location that is given as an input parameter to the method

int getValueFromArray(int *array, int len, int index) { 
 
int value; 
 
// check that the array index is less than the maximum 
// length of the array 
if (index < len) { 
 
// get the value at the specified index of the array 
value = array[index]; 
 
} 
// if array index is invalid then output error message 
// and return value indicating error 
else { 
printf("Value is: %d\n", array[index]); 
value = -1; 
 
} 
 
return value; 
 
} 

However, this method only verifies that the given array index is less than the maximum length of the array but does not check for the minimum value (CWE-839). This will allow a negative value to be accepted as the input array index, which will result in a out of bounds read (CWE-125) and may allow access to sensitive memory. The input array index should be checked to verify that is within the maximum and minimum range required for the array (CWE-129). In this example the if statement should be modified to include a minimum range check, as shown below.

... 
 
// check that the array index is within the correct 
// range of values for the array 
if (index <= 0 && index < len) { 
 
... 
2013/05/30 09:37

Observed Examples

Reference Description
CVE-2009-2550Classic stack-based buffer overflow in media player using a long entry in a playlist
CVE-2009-2403Heap-based buffer overflow in media player using a long entry in a playlist
CVE-2009-0689large precision value in a format string triggers overflow
CVE-2009-0690negative offset value leads to out-of-bounds read
CVE-2009-1532malformed inputs cause accesses of uninitialized or previously-deleted objects, leading to memory corruption
CVE-2009-1528chain: lack of synchronization leads to memory corruption
CVE-2009-0558attacker-controlled array index leads to code execution
CVE-2009-0269chain: -1 value from a function call was intended to indicate an error, but is used as an array index instead.
CVE-2009-0566chain: incorrect calculations lead to incorrect pointer dereference and memory corruption
CVE-2009-1350product accepts crafted messages that lead to a dereference of an arbitrary pointer
CVE-2009-0191chain: malformed input causes dereference of uninitialized memory
CVE-2008-4113OS kernel trusts userland-supplied length value, allowing reading of sensitive information
cwe/cn/definition/119.txt · 最后更改: 2014/09/04 14:24 (外部编辑)