Description
The product reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer.
Potential Impact
Confidentiality
Read Memory
Confidentiality
Bypass Protection Mechanism
Availability, Integrity
DoS: Crash, Exit, or Restart
Demonstrative Examples
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
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 (msgLength) from the structure is used as the condition for ending the for loop without validating that msgLength accurately reflects the actual length of the message body (CWE-606). If msgLength indicates a length that is longer than the size of a message body (CWE-130), then this can result in a buffer over-read by reading past the end of the buffer (CWE-126).
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
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
/* 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';Detection Methods
- Automated Static Analysis High — 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 sea
- Automated Dynamic Analysis Moderate — Use tools that are integrated during compilation to insert runtime error-checking mechanisms related to memory safety errors, such as AddressSanitizer (ASan) for C/C++ [REF-1518].
Real-World CVE Examples
| CVE ID | Description |
|---|---|
| CVE-2022-1733 | Text editor has out-of-bounds read past end of line while indenting C code |
| 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 |
| 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. |
Related Weaknesses
Taxonomy Mappings
- PLOVER: — Buffer over-read
- Software Fault Patterns: SFP8 — Faulty Buffer Access
Frequently Asked Questions
What is CWE-126?
CWE-126 (Buffer Over-read) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. The product reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer.
How can CWE-126 be exploited?
Attackers can exploit CWE-126 (Buffer Over-read) to read memory. This weakness is typically introduced during the Implementation phase of software development.
How do I prevent CWE-126?
Follow secure coding practices, conduct code reviews, and use automated security testing tools (SAST/DAST) to detect this weakness early in the development lifecycle.
What is the severity of CWE-126?
CWE-126 is classified as a Variant-level weakness (Low-Medium abstraction). It has been observed in 3 real-world CVEs.