CWE-788 在缓冲区结束位置之后访问内存

Access of Memory Location After End of Buffer

结构: Simple

Abstraction: Base

状态: Incomplete

被利用可能性: unkown

基本描述

The software reads or writes to a buffer using an index or pointer that references a memory location after the end of the buffer.

扩展描述

This typically occurs when a pointer or its index is decremented to a position before the buffer; when pointer arithmetic results in a position before the buffer; or when a negative index is used, which generates a position before the buffer.

相关缺陷

  • cwe_Nature: ChildOf cwe_CWE_ID: 119 cwe_View_ID: 1000 cwe_Ordinal: Primary

  • cwe_Nature: ChildOf cwe_CWE_ID: 119 cwe_View_ID: 699 cwe_Ordinal: Primary

常见的影响

范围 影响 注释
Confidentiality Read Memory For 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.
['Integrity', 'Availability'] ['Modify Memory', 'DoS: Crash, Exit, or Restart'] 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.
Integrity ['Modify Memory', 'Execute Unauthorized Code or Commands'] 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), they can redirect a function pointer to their 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.

示例代码

例

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.

bad C

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);
}

This function allocates a buffer of 64 bytes to store the hostname, however there is no guarantee that the hostname will not be larger than 64 bytes. If an attacker specifies an address which resolves to a very large hostname, then we may overwrite sensitive data or even relinquish control flow to the attacker.

Note that this example also contains an unchecked return value (CWE-252) that can lead to a NULL pointer dereference (CWE-476).

例

In the following example, it is possible to request that memcpy move a much larger segment of memory than assumed:

bad C

int returnChunkSize(void ) {

/ if chunk info is valid, return the size of usable memory,

else, return -1 to indicate an error

/
...
}
int main() {
...
memcpy(destBuf, srcBuf, (returnChunkSize(destBuf)-1));
...
}

If returnChunkSize() happens to encounter an error it will return -1. Notice that the return value is not checked before the memcpy operation (CWE-252), so -1 can be passed as the size argument to memcpy() (CWE-805). Because memcpy() assumes that the value is unsigned, it will be interpreted as MAXINT-1 (CWE-195), and therefore will copy far more memory than is likely available to the destination buffer (CWE-787, CWE-788).

例

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

bad C

char * copy_input(char user_supplied_string){
int i, dst_index;
char dst_buf = (char)malloc(4sizeof(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.

例

In the following C/C++ example the method processMessageFromSocket() will get a message from a socket, placed into a buffer, and will parse the contents of the buffer into a structure that contains the message length and the message body. A for loop is used to copy the message body into a local character string which will be passed to another method for processing.

bad C

int processMessageFromSocket(int socket) {
int success;

char buffer[BUFFER_SIZE];
char message[MESSAGE_SIZE];

// get message from socket and store into buffer

//Ignoring possibliity that buffer > BUFFER_SIZE
if (getMessage(socket, buffer, BUFFER_SIZE) > 0) {

// place contents of the buffer into message structure
ExMessage *msg = recastBuffer(buffer);

// copy message body into string for processing
int index;
for (index = 0; index < msg->msgLength; index++) {
message[index] = msg->msgBody[index];
}
message[index] = '\0';

// process message
success = processMessage(message);
}
return success;
}

However, the message length variable from the structure is used as the condition for ending the for loop without validating that the message length variable accurately reflects the length of message body. This can result in a buffer over read by reading from memory beyond the bounds of the buffer if the message length variable indicates a length that is longer than the size of a message body (CWE-130).

分析过的案例

标识 说明 链接
CVE-2009-2550 Classic stack-based buffer overflow in media player using a long entry in a playlist https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-2550
CVE-2009-2403 Heap-based buffer overflow in media player using a long entry in a playlist https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-2403
CVE-2009-0689 large precision value in a format string triggers overflow https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-0689
CVE-2009-0558 attacker-controlled array index leads to code execution https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-0558
CVE-2008-4113 OS kernel trusts userland-supplied length value, allowing reading of sensitive information https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-4113
CVE-2007-4268 Chain: integer signedness error (CWE-195) passes signed comparison, leading to heap overflow (CWE-122) https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-4268

分类映射

映射的分类名 ImNode ID Fit Mapped Node Name
OMG ASCRM ASCRM-CWE-788

引用