CVE Vulnerabilities

CVE-2021-20261

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Published: Mar 11, 2021 | Modified: Mar 19, 2021
CVSS 3.x
6.4
MEDIUM
Source:
NVD
CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
CVSS 2.x
4.4 MEDIUM
AV:L/AC:M/Au:N/C:P/I:P/A:P
RedHat/V2
RedHat/V3
6.7 MODERATE
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Ubuntu

A race condition was found in the Linux kernels implementation of the floppy disk drive controller driver software. The impact of this issue is lessened by the fact that the default permissions on the floppy device (/dev/fd0) are restricted to root. If the permissions on the device have changed the impact changes greatly. In the default configuration root (or equivalent) permissions are required to attack this flaw.

Weakness

The program contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently.

Affected Software

Name Vendor Start Version End Version
Linux_kernel Linux * *
Linux_kernel Linux 4.5 4.5
Linux_kernel Linux 4.5 4.5
Linux_kernel Linux 4.5 4.5
Linux_kernel Linux 4.5 4.5
Linux_kernel Linux 4.5 4.5
Linux Ubuntu esm-infra/xenial *
Linux Ubuntu precise/esm *
Linux Ubuntu trusty *
Linux Ubuntu trusty/esm *
Linux Ubuntu upstream *
Linux Ubuntu xenial *
Linux-aws Ubuntu esm-infra/xenial *
Linux-aws Ubuntu trusty *
Linux-aws Ubuntu trusty/esm *
Linux-aws Ubuntu upstream *
Linux-aws Ubuntu xenial *
Linux-aws-5.0 Ubuntu bionic *
Linux-aws-5.0 Ubuntu upstream *
Linux-aws-5.3 Ubuntu bionic *
Linux-aws-5.3 Ubuntu upstream *
Linux-aws-5.4 Ubuntu upstream *
Linux-aws-hwe Ubuntu upstream *
Linux-azure Ubuntu bionic *
Linux-azure Ubuntu trusty *
Linux-azure Ubuntu trusty/esm *
Linux-azure Ubuntu upstream *
Linux-azure-4.15 Ubuntu upstream *
Linux-azure-5.3 Ubuntu bionic *
Linux-azure-5.3 Ubuntu upstream *
Linux-azure-5.4 Ubuntu upstream *
Linux-azure-edge Ubuntu bionic *
Linux-azure-edge Ubuntu upstream *
Linux-dell300x Ubuntu upstream *
Linux-gcp Ubuntu bionic *
Linux-gcp Ubuntu upstream *
Linux-gcp-4.15 Ubuntu upstream *
Linux-gcp-5.3 Ubuntu bionic *
Linux-gcp-5.3 Ubuntu upstream *
Linux-gcp-5.4 Ubuntu upstream *
Linux-gcp-edge Ubuntu bionic *
Linux-gcp-edge Ubuntu upstream *
Linux-gke-4.15 Ubuntu bionic *
Linux-gke-4.15 Ubuntu upstream *
Linux-gke-5.0 Ubuntu bionic *
Linux-gke-5.0 Ubuntu upstream *
Linux-gke-5.3 Ubuntu upstream *
Linux-gke-5.4 Ubuntu upstream *
Linux-gkeop Ubuntu upstream *
Linux-gkeop-5.4 Ubuntu upstream *
Linux-hwe Ubuntu bionic *
Linux-hwe Ubuntu upstream *
Linux-hwe-5.4 Ubuntu upstream *
Linux-hwe-5.8 Ubuntu upstream *
Linux-hwe-edge Ubuntu bionic *
Linux-hwe-edge Ubuntu esm-infra/xenial *
Linux-hwe-edge Ubuntu upstream *
Linux-hwe-edge Ubuntu xenial *
Linux-kvm Ubuntu esm-infra/xenial *
Linux-kvm Ubuntu upstream *
Linux-kvm Ubuntu xenial *
Linux-lts-trusty Ubuntu precise/esm *
Linux-lts-trusty Ubuntu upstream *
Linux-lts-xenial Ubuntu trusty *
Linux-lts-xenial Ubuntu trusty/esm *
Linux-lts-xenial Ubuntu upstream *
Linux-oem Ubuntu bionic *
Linux-oem Ubuntu upstream *
Linux-oem Ubuntu xenial *
Linux-oem-5.10 Ubuntu upstream *
Linux-oem-5.6 Ubuntu upstream *
Linux-oem-osp1 Ubuntu bionic *
Linux-oem-osp1 Ubuntu upstream *
Linux-oracle Ubuntu upstream *
Linux-oracle-5.0 Ubuntu bionic *
Linux-oracle-5.0 Ubuntu upstream *
Linux-oracle-5.3 Ubuntu bionic *
Linux-oracle-5.3 Ubuntu upstream *
Linux-oracle-5.4 Ubuntu upstream *
Linux-raspi Ubuntu upstream *
Linux-raspi-5.4 Ubuntu upstream *
Linux-raspi2 Ubuntu focal *
Linux-raspi2 Ubuntu upstream *
Linux-raspi2 Ubuntu xenial *
Linux-raspi2-5.3 Ubuntu upstream *
Linux-riscv Ubuntu focal *
Linux-riscv Ubuntu upstream *
Linux-snapdragon Ubuntu bionic *
Linux-snapdragon Ubuntu upstream *
Linux-snapdragon Ubuntu xenial *

Extended Description

This can have security implications when the expected synchronization is in security-critical code, such as recording whether a user is authenticated or modifying important state information that should not be influenced by an outsider. A race condition occurs within concurrent environments, and is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. Programmers may assume that certain code sequences execute too quickly to be affected by an interfering code sequence; when they are not, this violates atomicity. For example, the single “x++” statement may appear atomic at the code layer, but it is actually non-atomic at the instruction layer, since it involves a read (the original value of x), followed by a computation (x+1), followed by a write (save the result to x). The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the program; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable program.

Potential Mitigations

  • Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
  • Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

References