CVE-2020-14416
Description
A use-after-free flaw was found in slcan_write_wakeup in drivers/net/can/slcan.c in the serial CAN module slcan. A race condition occurs when communicating with can using slcan between the write (scheduling the transmit) and closing (flushing out any pending queues) the SLCAN channel. This flaw allows a local attacker with special user or root privileges to cause a denial of service or a kernel information leak. The highest threat from this vulnerability is to system availability.
Mitigation
Mitigation for this issue is to skip loading the affected module 'slcan' and 'slip' onto the system until a fix is available. Using a blacklist mechanism will ensure the driver is not loaded at boot time and requires specific hardware (CANbus hardware), which is not in use on the system.
How do I blacklist a kernel module to prevent it from loading automatically?
https://access.redhat.com/solutions/41278
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 | 4.2 | 4.2 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | High | High | N/A |
| User Interaction | Required | Required | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:H/UI:R/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:H/UI:R/S:U/C:N/I:N/A:H
Red Hat CVSS v3 Score Explanation
- Attacker will need a local access (AV:L) to write on the serial interface.
- This will need a special user privilege (PR:H) or root to talk to simply (AC:L)
- Attacker to exploit this, will have to close the SLCAN channel while write and when 'tty->disc_data' races to NULL (while write) will cause a denial of service (DoS) in form of UAF problem (UI:R)
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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