CVE-2021-38199
Description
A flaw was found in the hanging of mounts in the Linux kernel's NFS4 subsystem where remote servers are unreachable for the client during migration of data from one server to another (during trunking detection). This flaw allows a remote NFS4 server (if the client is connected) to starve the resources, causing a denial of service. The highest threat from this vulnerability is to system availability.
Statement
This flaw is rated as having a Low impact because the known scenario of attack doesn't allow denial of service for the NFS itself, but only potentially does denial of service for some applications that can fail during remount after NFS mounts temporary fail (and both because this kind of attacks like from some network service server to the client with drop connection or similar doesn't look like something that client not-safe for, and as result this type of attacks should not be considered as sensitive severity impact).
Mitigation
If not using NFS, then to mitigate this issue, prevent the module nfsv4 from being loaded. Please see https://access.redhat.com/solutions/41278 for information on how to blacklist a kernel module to prevent it from loading automatically.
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 | 6.5 | 6.5 | N/A |
| Attack Vector | Adjacent Network | Adjacent Network | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | 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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Red Hat CVSS v3 Score Explanation
The attack vector is adjacent , because first need to open connection, so the vulnerability cannot be triggered remotely if no existing connection (and if can be triggered only between authorized existing connections, then more likely adjacent than network).
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory; Read Application Data
When reusing a resource such as memory or a program variable, the original contents of that resource may not be cleared before it is sent to an untrusted party.
Access Control
Technical Impact: Bypass Protection Mechanism
If security-critical decisions rely on a variable having a "0" or equivalent value, and the programming language performs this initialization on behalf of the programmer, then a bypass of security may occur.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
The uninitialized data may contain values that cause program flow to change in ways that the programmer did not intend. For example, if an uninitialized variable is used as an array index in C, then its previous contents may produce an index that is outside the range of the array, possibly causing a crash or an exit in other environments.
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