CVE-2020-12887 Information

Description

Memory leaks were discovered in the CoAP library in Arm Mbed OS 5.15.3 when using the Arm mbed-coap library 5.1.5. The CoAP parser is responsible for parsing received CoAP packets. The function sn_coap_parser_options_parse() parses the CoAP option number field of all options present in the input packet. Each option number is calculated as a sum of the previous option number and a delta of the current option. The delta and the previous option number are expressed as unsigned 16-bit integers. Due to lack of overflow detection it is possible to craft a packet that wraps the option number around and results in the same option number being processed again in a single packet. Certain options allocate memory by calling a memory allocation function. In the cases of COAP_OPTION_URI_QUERY COAP_OPTION_URI_PATH COAP_OPTION_LOCATION_QUERY and COAP_OPTION_ETAG there is no check on whether memory has already been allocated which in conjunction with the option number integer overflow may lead to multiple assignments of allocated memory to a single pointer. This has been demonstrated to lead to memory leak by buffer orphaning. As a result the memory is never freed.

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Reference

https://github.com/ARMmbed/mbed-coap/pull/116 https://github.com/ARMmbed/mbed-os/issues/12930 https://github.com/ARMmbed/mbed-os/issues/12957 https://github.com/mjurczak/mbed-coap/commit/4647a68e364401e81dbd370728127d844f221d93

Attack Complexity

LOW

Privileges Required

NONE

User Interaction Required

NONE

Scope

NONE

Confidentiality Impact

UNCHANGED

Integrity Impact

NONE

Availability Impact

NONE

Base Score

HIGH

Base Severity

7.5