CWE-126 缓冲区上溢读取

Buffer Over-read

结构: Simple

Abstraction: Variant

状态: Draft

被利用可能性: unkown

基本描述

The software reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer.

扩展描述

This typically occurs when the pointer or its index is incremented to a position beyond the bounds of the buffer or when pointer arithmetic results in a position outside of the valid memory location to name a few. This may result in exposure of sensitive information or possibly a crash.

适用平台

Language: [{'cwe_Name': 'C', 'cwe_Prevalence': 'Undetermined'}, {'cwe_Name': 'C++', 'cwe_Prevalence': 'Undetermined'}]

常见的影响

范围	影响	注释
Confidentiality	Read Memory
Confidentiality	Bypass Protection Mechanism	By reading out-of-bounds memory, an attacker might be able to get secret values, such as memory addresses, which can be bypass protection mechanisms such as ASLR in order to improve the reliability and likelihood of exploiting a separate weakness to achieve code execution instead of just denial of service.

示例代码

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).

例

The following C/C++ example demonstrates a buffer over-read due to a missing NULL terminator. The main method of a pattern matching utility that looks for a specific pattern within a specific file uses the string strncopy() method to copy the command line user input file name and pattern to the Filename and Pattern character arrays respectively.

bad C

int main(int argc, char argv)
{

char Filename[256];
char Pattern[32];

/ Validate number of parameters and ensure valid content /
...

/ copy filename parameter to variable, may cause off-by-one overflow /
strncpy(Filename, argv[1], sizeof(Filename));

/ copy pattern parameter to variable, may cause off-by-one overflow /
strncpy(Pattern, argv[2], sizeof(Pattern));

printf("Searching file: %s for the pattern: %s\n", Filename, Pattern);
Scan_File(Filename, Pattern);

}

However, the code do not take into account that strncpy() will not add a NULL terminator when the source buffer is equal in length of longer than that provide size attribute. Therefore if a user enters a filename or pattern that are the same size as (or larger than) their respective character arrays, a NULL terminator will not be added (CWE-170) which leads to the printf() read beyond the expected end of the Filename and Pattern buffers.

To fix this problem, be sure to subtract 1 from the sizeof() call to allow room for the null byte to be added.

good C

/ copy filename parameter to variable, no off-by-one overflow /
strncpy(Filename, argv[2], sizeof(Filename)-1);
Filename[255]='\0';

/ copy pattern parameter to variable, no off-by-one overflow /
strncpy(Pattern, argv[3], sizeof(Pattern)-1);

Pattern[31]='\0';

分析过的案例

标识	说明	链接
CVE-2014-0160	Chain: "Heartbleed" bug receives an inconsistent length parameter (CWE-130) enabling an out-of-bounds read (CWE-126), returning memory that could include private cryptographic keys and other sensitive data.	https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-0160
CVE-2009-2523	Chain: product does not handle when an input string is not NULL terminated, leading to buffer over-read or heap-based buffer overflow.	https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-2523

Notes

分类映射

映射的分类名	ImNode ID	Fit	Mapped Node Name
PLOVER			Buffer over-read
Software Fault Patterns	SFP8		Faulty Buffer Access

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