CVE-2019-19378
Description
A flaw was found in the BTRFS implementation in the Linux kernel. A slab-out-of-bounds write occurs when an attacker can mount a specially crafted BTRFS disk or disk image.
Statement
This issue is considered as having Low impact because it needs physical access to trigger and it's also in Technology Preview functionality. For more information regarding BTRFS support in Red Hat Enterprise Linux 6 and 7 refer to https://access.redhat.com/solutions/197643 .
Mitigation
As the BTRFS module will be auto-loaded when required, its use can be disabled by preventing the module from loading with the following instructions:
# echo "install btrfs /bin/true" >> /etc/modprobe.d/disable-btrfs.conf
The system will need to be restarted if the BTRFS modules are loaded, it may be possible to unload them. In most circumstances, the BTRFS kernel modules will be unable to be unloaded while any BTRFS filesystems are mounted or in use.
If the system requires this module to work correctly, this mitigation may not be suitable.
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 | 7.8 | 7.8 | 7.8 |
| Attack Vector | Local | Local | Local |
| Attack Complexity | Low | Low | Low |
| Privileges Required | None | None | None |
| User Interaction | Required | Required | Required |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | High | High | High |
| Integrity Impact | High | High | High |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Red Hat CVSS v3 Score Explanation
In this case, the write seems to be to another entry on the slab, while this is not controlled a dedicated attacker could align this to a value needed to be manipulated.
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Write operations could cause memory corruption. In some cases, an adversary can modify control data such as return addresses in order to execute unexpected code.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
Attempting to access out-of-range, invalid, or unauthorized memory could cause the product to crash.
Other
Technical Impact: Unexpected State
Subsequent write operations can produce undefined or unexpected results.
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