325
Scope Impact Likelihood
Availability Modify Memory
Many memory accesses can lead to program termination,
such as when writing to addresses that are invalid for the
current process.
Access Control
Other
Bypass Protection Mechanism
Other
When the consequence is arbitrary code execution, this
can often be used to subvert any other security service.
Potential Mitigations
Phase: Architecture and Design
Strategy = Language Selection
Use a language that provides appropriate memory abstractions.
Phase: Operation
Use OS-level preventative functionality integrated after the fact. Not a complete solution.
Demonstrative Examples
Example 1:
The classic example of a write-what-where condition occurs when the accounting information
for memory allocations is overwritten in a particular fashion. Here is an example of potentially
vulnerable code:
Example Language: C (Bad)
#define BUFSIZE 256
int main(int argc, char **argv) {
char *buf1 = (char *) malloc(BUFSIZE);
char *buf2 = (char *) malloc(BUFSIZE);
strcpy(buf1, argv[1]);
free(buf2);
}
Vulnerability in this case is dependent on memory layout. The call to strcpy() can be used to write
past the end of buf1, and, with a typical layout, can overwrite the accounting information that
the system keeps for buf2 when it is allocated. Note that if the allocation header for buf2 can be
overwritten, buf2 itself can be overwritten as well.
The allocation header will generally keep a linked list of memory "chunks". Particularly, there may
be a "previous" chunk and a "next" chunk. Here, the previous chunk for buf2 will probably be buf1,
and the next chunk may be null. When the free() occurs, most memory allocators will rewrite the
linked list using data from buf2. Particularly, the "next" chunk for buf1 will be updated and the
"previous" chunk for any subsequent chunk will be updated. The attacker can insert a memory
address for the "next" chunk and a value to write into that memory address for the "previous"
chunk.
This could be used to overwrite a function pointer that gets dereferenced later, replacing it with
a memory address that the attacker has legitimate access to, where they have placed malicious
code, resulting in arbitrary code execution.
Observed Examples
Reference Description
CVE-2022-21668 Chain: Python library does not limit the resources used to process images
that specify a very large number of bands (CWE-1284), leading to excessive
memory consumption (CWE-789) or an integer overflow (CWE-190).
CWE Version 4.14
CWE-124: Buffer Underwrite ('Buffer Underflow')
CWE-124: Buffer Underwrite ('Buffer Underflow')