An issue was discovered in MBed OS 6.16.0. During processing of HCI packets, the software dynamically determines the length of the packet data by reading 2 bytes from the packet header. A buffer is then allocated to contain the entire packet, the size of which is calculated as the length of the packet body determined earlier plus the header length. WsfMsgAlloc then increments this again by sizeof(wsfMsg_t). This may cause an integer overflow that results in the buffer being significantly too small to contain the entire packet. This may cause a buffer overflow of up to 65 KB . This bug is trivial to exploit for a denial of service but can generally not be exploited further because the exploitable buffer is dynamically allocated.
Weakness
The product performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control.
Affected Software
| Name |
Vendor |
Start Version |
End Version |
| Mbed |
Arm |
6.16.0 (including) |
6.16.0 (including) |
Potential Mitigations
- Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
- If possible, choose a language or compiler that performs automatic bounds checking.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
- Use libraries or frameworks that make it easier to handle numbers without unexpected consequences.
- Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++). [REF-106]
- Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.
- Use unsigned integers where possible. This makes it easier to perform validation for integer overflows. When signed integers are required, ensure that the range check includes minimum values as well as maximum values.
- Understand the programming language’s underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, “not-a-number” calculations, and how the language handles numbers that are too large or too small for its underlying representation. [REF-7]
- Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.
References