CVE-2019-19529
Description
A use-after-free flaw was found in the driver for the USB Microchip CAN BUS Analyzer Tool. The CAN BUS analysis hardware is not commonly found on server-grade hardware where the flaw exists while a device is removed (physical access) or a kernel module is unloaded (administrative privileges). An attacker must race the code while the device is being unplugged to take advantage of this flaw.
Mitigation
As the mcba_usb odule will be auto-loaded when required, its use can be disabled by preventing the module from loading with the following instructions:
# echo "install mcba_usb /bin/true" >> /etc/modprobe.d/disable-mcba_usb.conf
The system will need to be restarted in the unlikely case that the modules are loaded. In most circumstances, the kernel modules will be unable to be unloaded with rmmod while any device has the software in use.
If the system requires this module to work correctly, this mitigation may not be suitable, alternative USB can analysers will not suffer this same flaw.
If you need further assistance, see KCS article https://access.redhat.com/solutions/41278 or contact Red Hat Global Support Services.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.3 | 6.3 | N/A |
| Attack Vector | Physical | Physical | N/A |
| Attack Complexity | High | High | N/A |
| Privileges Required | Low | Low | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:P/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:P/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Red Hat CVSS v3 Score Explanation
There are two possible ways to trigger this flaw, physical and local. If the attacker is to trigger it with physical access they must also have a local account (PR:L) to pre-groom the memory to take advantage of this flaw. After that point it may be possible to use the pre-groomed memory to escalate privileges.
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory
The use of previously freed memory may corrupt valid data, if the memory area in question has been allocated and used properly elsewhere.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If chunk consolidation occurs after the use of previously freed data, the process may crash when invalid data is used as chunk information.
Confidentiality
Technical Impact: Read Memory
Read operations on freed memory can sometimes leak sensitive information instead of causing a crash
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If malicious data is entered before chunk consolidation can take place, it may be possible to take advantage of a write-what-where primitive to execute arbitrary code. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.
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