CVE-2022-36063

Azure RTOS USBx is a USB host, device, and on-the-go (OTG) embedded stack, fully integrated with Azure RTOS ThreadX and available for all Azure RTOS ThreadX–supported processors. Azure RTOS USBX implementation of host support for USB CDC ECM includes an integer underflow and a buffer overflow in the _ux_host_class_cdc_ecm_mac_address_get function which may be potentially exploited to achieve remote code execution or denial of service. Setting mac address string descriptor length to a 0 or 1 allows an attacker to introduce an integer underflow followed (string_length) by a buffer overflow of the cdc_ecm -> ux_host_class_cdc_ecm_node_id array. This may allow one to redirect the code execution flow or introduce a denial of service. The fix has been included in USBX release 6.1.12. Improved mac address string descriptor length validation to check for unexpectedly small values may be used as a workaround.

Weakness

The product receives input that is expected to specify a quantity (such as size or length), but it does not validate or incorrectly validates that the quantity has the required properties.

Affected Software

Extended Description

Specified quantities include size, length, frequency, price, rate, number of operations, time, and others. Code may rely on specified quantities to allocate resources, perform calculations, control iteration, etc. When the quantity is not properly validated, then attackers can specify malicious quantities to cause excessive resource allocation, trigger unexpected failures, enable buffer overflows, etc.

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

References

• https://github.com/azure-rtos/usbx/blob/master/common/usbx_host_classes/src/ux_host_class_cdc_ecm_mac_address_get.c#L264
• https://github.com/azure-rtos/usbx/releases/tag/v6.1.12_rel
• https://github.com/azure-rtos/usbx/security/advisories/GHSA-chpp-5fv9-6368