Memory Allocation with Excessive Size Value
The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated.
The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.
Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.
Consider the following code, which accepts an untrusted size value and allocates a buffer to contain a string of the given size.
Suppose an attacker provides a size value of:
This will cause 305,419,896 bytes (over 291 megabytes) to be allocated for the string.
Consider the following code, which accepts an untrusted size value and uses the size as an initial capacity for a HashMap.
The HashMap constructor will verify that the initial capacity is not negative, however there is no check in place to verify that sufficient memory is present. If the attacker provides a large enough value, the application will run into an OutOfMemoryError.
This code performs a stack allocation based on a length calculation.
Since a and b are declared as signed ints, the "a - b" subtraction gives a negative result (-1). However, since len is declared to be unsigned, len is cast to an extremely large positive number (on 32-bit systems - 4294967295). As a result, the buffer buf[len] declaration uses an extremely large size to allocate on the stack, very likely more than the entire computer's memory space.
Miscalculations usually will not be so obvious. The calculation will either be complicated or the result of an attacker's input to attain the negative value.
This example shows a typical attempt to parse a string with an error resulting from a difference in assumptions between the caller to a function and the function's action.
The buffer length ends up being -1, resulting in a blown out stack. The space character after the colon is included in the function calculation, but not in the caller's calculation. This, unfortunately, is not usually so obvious but exists in an obtuse series of calculations.
The following code obtains an untrusted number that is used as an index into an array of messages.
The index is not validated at all (CWE-129), so it might be possible for an attacker to modify an element in @messages that was not intended. If an index is used that is larger than the current size of the array, the Perl interpreter automatically expands the array so that the large index works.
If $num is a large value such as 2147483648 (1<<31), then the assignment to $messages[$num] would attempt to create a very large array, then eventually produce an error message such as:
Out of memory during array extend
This memory exhaustion will cause the Perl program to exit, possibly a denial of service. In addition, the lack of memory could also prevent many other programs from successfully running on the system.
This example shows a typical attempt to parse a string with an error resulting from a difference in assumptions between the caller to a function and the function's action. The buffer length ends up being -1 resulting in a blown out stack. The space character after the colon is included in the function calculation, but not in the caller's calculation. This, unfortunately, is not usually so obvious but exists in an obtuse series of calculations.
Weaknesses in this category are related to memory safety.
Weaknesses in this category are related to the CISQ Quality Measures for Security. Presence of these weaknesses could reduce the security of the software.
Weaknesses in this category are related to the rules and recommendations in the Input Validation and Data Sanitization (IDS) section of the SEI CERT Perl Coding Standard.
This view (slice) covers all the elements in CWE.
This view (slice) lists weaknesses that can be introduced during implementation.
This view (slice) covers issues that are found in C++ programs that are not common to all languages.