Vulnerabilities
Misconfiguration
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CVE Vulnerabilities

CVE-2021-4207

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

Published: Apr 29, 2022 | Modified: Mar 21, 2025
CVSS 3.x
8.2
HIGH
Source:
NVD
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H
CVSS 2.x
4.6 MEDIUM
AV:L/AC:L/Au:N/C:P/I:P/A:P
RedHat/V2
RedHat/V3
7.5 MODERATE
CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
Ubuntu
MEDIUM
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Additional information
NVDhttps://nvd.nist.gov/vuln/detail/CVE-2021-4207
CWEhttps://cwe.mitre.org/data/definitions/362.html

A flaw was found in the QXL display device emulation in QEMU. A double fetch of guest controlled values cursor->header.width and cursor->header.height can lead to the allocation of a small cursor object followed by a subsequent heap-based buffer overflow. A malicious privileged guest user could use this flaw to crash the QEMU process on the host or potentially execute arbitrary code within the context of the QEMU process.

Weakness

The product contains a concurrent code sequence that 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 operating concurrently.

Affected Software

NameVendorStart VersionEnd Version
QemuQemu*7.0.0 (excluding)
Advanced Virtualization for RHEL 8.4.0.EUSRedHatvirt:av-8040020220517095834.522a0ee4*
Advanced Virtualization for RHEL 8.4.0.EUSRedHatvirt-devel:av-8040020220517095834.522a0ee4*
Red Hat Enterprise Linux 8RedHatvirt-devel:rhel-8060020220616155742.ad008a3a*
Red Hat Enterprise Linux 8RedHatvirt:rhel-8060020220616155742.ad008a3a*
QemuUbuntubionic*
QemuUbuntudevel*
QemuUbuntuesm-infra/bionic*
QemuUbuntuesm-infra/focal*
QemuUbuntufocal*
QemuUbuntuimpish*
QemuUbuntujammy*
QemuUbuntukinetic*
QemuUbuntulunar*
QemuUbuntumantic*
QemuUbuntunoble*
QemuUbuntuoracular*
QemuUbuntuplucky*
QemuUbuntuquesting*
QemuUbuntutrusty*
QemuUbuntutrusty/esm*
QemuUbuntuxenial*

Extended Description

A race condition occurs within concurrent environments, and it 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. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; 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 product.

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

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