CVE-2019-15920
Description
An issue was discovered in the Linux kernel's implementation of the CIFS protocol. The SMB2_read function has a possible use-after-free when CIFS function tracing is enabled. While data is used after being freed, it is has not been determined how it could be used for privilege escalation.
Mitigation
As the CIFS module will be auto-loaded when required, its use can be disabled
by preventing the module from loading with the following instructions:
# echo "install cifs /bin/true" >> /etc/modprobe.d/disable-cifs.conf
The system will need to be restarted if the CIFS modules are loaded. In most circumstances, the CIFS kernel modules will be unable to be unloaded while any network interfaces are active and the protocol is in use.
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).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 3.3 | 4.3 | N/A |
| Attack Vector | Local | Network | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | Low | Low | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | Low | Low | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Red Hat CVSS v3 Score Explanation
The 'attack' vector while in a networked component does not not use network specific information. The data that is used-after-free is not attacker information and from inspection can't be used for a privesc attack.
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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