CVE-2021-20181

Name: CVE-2021-20181
Creator: NVD / NIST
Published: 2021-05-13T16:15:07.653+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 0.32%

Last modified Jun 17, 2026

CVE-2021-20181 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. A race condition flaw was found in the 9pfs server implementation of QEMU up to and including 5.2.0. This flaw allows a malicious 9p client to cause a use-after-free error, potentially escalating their privileges on the system. EPSS estimates a 0.32% chance of exploitation in the next 30 days.

Description

A race condition flaw was found in the 9pfs server implementation of QEMU up to and including 5.2.0. This flaw allows a malicious 9p client to cause a use-after-free error, potentially escalating their privileges on the system. The highest threat from this vulnerability is to confidentiality, integrity as well as system availability.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

EPSS Probability

0.32%

23.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Qemu	Qemu	<= 5.2.0
Debian	Debian Linux	9.0
Debian	Debian Linux	10.0

References

https://bugzilla.redhat.com/show_bug.cgi?id=1927007Issue Tracking, Patch, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2021/02/msg00024.htmlMailing List, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/09/msg00008.htmlMailing List, Third Party Advisory
https://security.netapp.com/advisory/ntap-20210720-0009/Third Party Advisory
https://www.zerodayinitiative.com/advisories/ZDI-21-159/Third Party Advisory, VDB Entry
https://bugzilla.redhat.com/show_bug.cgi?id=1927007Issue Tracking, Patch, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2021/02/msg00024.htmlMailing List, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/09/msg00008.htmlMailing List, Third Party Advisory
https://security.netapp.com/advisory/ntap-20210720-0009/Third Party Advisory
https://www.zerodayinitiative.com/advisories/ZDI-21-159/Third Party Advisory, VDB Entry

Timeline

Published: May 13, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-20181?

How severe is CVE-2021-20181?

CVE-2021-20181 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.32% probability of exploitation in the next 30 days.

How do I fix CVE-2021-20181?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-20181?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST