CVE-2021-20181: debian debian_linux
Vulnerability summary
CVE-2021-20181 is a high (CVSS 7.5) vulnerability in debian debian_linux. EPSS estimates a 0.33% chance of exploitation in the next 30 days, higher than 26.5% of scored vulnerabilities.
Not severe (CVSS 7.5, local access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 14 · Related 13Timeline
- 13-05-2021PublishedVulnerability first disclosed.
- 03-08-2024Last modifiedVulnerability information updated.
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.
CVSS metrics
5 scores · 4 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated7.5HighCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
- OSV · DebianEcosystem advisory · calculated7.5HighCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
- OSV · AlpineEcosystem advisory · calculated7.5HighCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
EPSS trend
Probability
0.33%
Chance of exploitation in the next 30 days
Percentile
27%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.33% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-367Time-of-check Time-of-use (TOCTOU) Race ConditionThe product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.
- CWE-362Concurrent Execution using Shared Resource with Improper SynchronizationThe 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 systems
Known conditions: local access, administrative account, no user interaction (CVSS vector). Other conditions: not stated in public data.
Debian2 products
- qemu< 1:5.2+dfsg-4
- debian_linuxEOL9.0 | 10.0
Alpine1 product
- qemu< 6.0.0-r1
Qemu1 product
- qemu≤ 5.2.0
Ubuntu1 product
- qemu< 2.0.0+dfsg-2ubuntu1.47+esm6 | < 1:2.5+dfsg-5ubuntu10.49 | < 1:2.11+dfsg-1ubuntu7.35 | < 1:4.2-3ubuntu6.12
4 vendors · 5 products
References
12 links
lists.debian.org/debian-lts-announce/2021/02/msg00024.htmlMailing ListX Refsource MLISTThird Party Advisory- lists.debian.org/debian-lts-announce/2022/09/msg00008.htmlMailing ListX Refsource MLISTThird Party Advisory
