CVE-2019-19816
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Description
A flaw was found in the implementation of the BTRFS file system code in the Linux kernel. An attacker, who is able to mount a crafted BTRFS filesystem and perform common filesystem operations, can possibly cause an out-of-bounds write to memory. This could lead to memory corruption or privilege escalation.
Statement
The vulnerability is considered moderate rather than important because it requires specific conditions to be exploited. An attacker must have physical access to the system and be able to mount a crafted BTRFS filesystem, which limits the potential attack vectors and also a local account to abuse the use-after-free. Additionally, the flaw involves an out-of-bounds write when handling RAID56 metadata, which could lead to memory corruption, but exploitation for privilege escalation is not straightforward due to mitigations like kernel address space layout randomization (KASLR). As a result, the impact is more constrained, affecting system stability rather than directly allowing unauthorized access or significant data compromise.
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.
Additional information
- Bugzilla 1784923: kernel: out-of-bounds write in __btrfs_map_block in fs/btrfs/volumes.c
- CWE-787: Out-of-bounds Write
- FAQ: Frequently asked questions about CVE-2019-19816
Common Vulnerability Scoring System (CVSS) Score Details
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.
| Red Hat | NVD | |
|---|---|---|
CVSS v3 Base Score | 7.8 | 7.8 |
Attack Vector | Local | Local |
Attack Complexity | Low | Low |
Privileges Required | None | None |
User Interaction | Required | Required |
Scope | Unchanged | Unchanged |
Confidentiality Impact | High | High |
Integrity Impact | High | High |
Availability Impact | High | High |
CVSS v3 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
Frequently Asked Questions
Why is Red Hat's CVSS v3 score or Impact different from other vendors?
For more information, see https://access.redhat.com/solutions/762393.
My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?
- "Under investigation" doesn't necessarily mean that the product is affected by this vulnerability. It only means that our Analysis Team is still working on determining whether the product is affected and how it is affected.
- The term "Affected" means that our Analysis team has determined that this product, such as Red Hat Enterprise Linux 8 or OpenShift Container Platform 4, is affected by this vulnerability and a fix may be released to address this issue in the near future. This includes all minor releases of this product unless noted otherwise in the Statement text.
What can I do if my product is listed as "Will not fix"?
Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
- Upgrade to a supported product version that includes a fix for this vulnerability (recommended).
- Apply a mitigation (if one exists).
- Open a support case to request a prioritization of releasing a fix for this vulnerability.
What can I do if my product is listed as "Fix deferred"?
Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
- Apply a mitigation (if one exists).
- Open a support case to request a prioritization of releasing a fix for this vulnerability.
- Red Hat Engineering focuses on addressing high-priority issues based on their complexity or limited lifecycle support. Therefore, lower-priority issues will not receive immediate fixes.
What is a mitigation?
I have a Red Hat product but it is not in the above list, is it affected?
Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?
My product is listed as "Out of Support Scope". What does this mean?
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