CWE-788: Access of Memory Location After End of Buffer

Code examples

Illustrative examples from MITRE showing how the weakness appears in code.

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.

Vulnerable example

void host_lookup(char *user_supplied_addr){

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

Vulnerable example

int returnChunkSize(void *) {

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).

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

Vulnerable example

char * copy_input(char *user_supplied_string){

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.

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.

Vulnerable example

int processMessageFromSocket(int socket) {

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).

CWE-788: Access of Memory Location After End of Buffer

Overview

Real-world CVEs

Common consequences

How it happens

When it is introduced

Applies to

How to detect it

Fuzzing

Automated Static Analysis

Automated Dynamic Analysis

Code examples

Illustrative examples

Terminology & mappings

Mapped taxonomies

Frequently asked questions

What is CWE-788?

What CVEs are caused by CWE-788?

How is CWE-788 detected?

What are the consequences of CWE-788?

Is CWE-788 actively exploited?

References

Stay ahead of CWE-788

Overview

Real-world CVEs

Common consequences

How it happens

When it is introduced

Applies to

How to detect it

Fuzzing

Automated Static Analysis

Automated Dynamic Analysis

Code examples

Illustrative examples

Related weaknesses

Parent

Child

Terminology & mappings

Mapped taxonomies

Frequently asked questions

What is CWE-788?

What CVEs are caused by CWE-788?

How is CWE-788 detected?

What are the consequences of CWE-788?

Is CWE-788 actively exploited?

References

Stay ahead of CWE-788