CVE-2021-20257

An infinite loop flaw was found in the e1000 NIC emulator of the QEMU. This issue occurs while processing transmits (tx) descriptors in process_tx_desc if various descriptor fields are initialized with invalid values. This flaw allows a guest to consume CPU cycles on the host, resulting in a denial of service. The highest threat from this vulnerability is to system availability.

Published: 2022-03-16 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-20257 is rated Low Risk (35.8/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.36%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-20257

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.10% 0.36% +0.25%
2 2025-10-12 0.04% 0.10% +0.06%
3 2023-03-07 — 0.04% —

Full EPSS history (7 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-20257

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.5 3.1 MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.0 4.0 [email protected]
2.1 2.0 LOW
AV:L/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:L)
Requires local access to the target system.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 3.9 2.9 [email protected]

Weakness enumeration for CVE-2021-20257

OS Trackers for CVE-2021-20257

vendor priority summary link
alpine medium CVE-2021-20257: 1 source package rows (qemu); 23 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 23. https://security.alpinelinux.org/vuln/CVE-2021-20257
debian not yet assigned CVE-2021-20257 not yet assigned priority: Debian including 1 source packages (qemu), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-20257
gentoo high CVE-2021-20257: 1 GLSA(s) (202208-27), 1 atom(s) (app-emulation/qemu); latest impact high. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-20257
redhat low — https://access.redhat.com/security/cve/CVE-2021-20257
suse low CVE-2021-20257 severity low: SUSE including 875 source package names (0.38.1.5.8.40:qemu-4.2.1-11.16.3, 0.38.1.5.8.40:qemu-ipxe-1.0.0+-11.16.3, …), 1591 product×package rows across 84 product lines (Container suse/sles/15.2/virt-handler, Container suse/sles/15.2/virt-launcher, … (84 product lines)): Fixed 1161, Known Affected 225, Known Not Affected 205. https://www.suse.com/security/cve/CVE-2021-20257/
ubuntu medium CVE-2021-20257 medium priority: Ubuntu including 2 source packages (qemu, qemu-kvm), 32 status rows across 16 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 15, not-affected 10, released 3, needed 2, needs-triage 2. https://ubuntu.com/security/CVE-2021-20257

Affected software / configurations for CVE-2021-20257

Vendor Product Version Raw CPE
qemu qemu < 6.2.0 cpe:2.3:a:qemu:qemu:*:*:*:*:*:*:*:*
fedoraproject fedora 33 cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
redhat openstack_platform 10.0 cpe:2.3:a:redhat:openstack_platform:10.0:*:*:*:*:*:*:*
redhat openstack_platform 13.0 cpe:2.3:a:redhat:openstack_platform:13.0:*:*:*:*:*:*:*
redhat enterprise_linux 6.0 cpe:2.3:o:redhat:enterprise_linux:6.0:*:*:*:*:*:*:*
redhat enterprise_linux 8.0 cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
redhat enterprise_linux 8.0 cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:advanced_virtualization:*:*:*
redhat enterprise_linux_for_ibm_z_systems 8.0 cpe:2.3:o:redhat:enterprise_linux_for_ibm_z_systems:8.0:*:*:*:*:*:*:*
redhat enterprise_linux_for_power_little_endian 8.0 cpe:2.3:o:redhat:enterprise_linux_for_power_little_endian:8.0:*:*:*:*:*:*:*
redhat codeready_linux_builder — cpe:2.3:a:redhat:codeready_linux_builder:-:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*

References for CVE-2021-20257

cvelogic Threat Intelligence