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Fencer Vulns
medium 6.5

CVE-2021-20257 json

An infinite loop flaw was found in the e1000 NIC emulator of the QEMU.

published 2022-03-16 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-7695

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 31%
public exploits
0
none known

Summary

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.

Patch / fix

  • qemu qemu 6.2.0
  • qemu Debian 14, Debian 13, Debian 12 1:5.2+dfsg-9

debian advisories DEBIAN-CVE-2021-20257

  • qemu Ubuntu 18.04 LTS 1:2.11+dfsg-1ubuntu7.37
  • qemu Ubuntu 20.04 LTS 1:4.2-3ubuntu6.17
  • qemu Ubuntu Pro 14.04 LTS 2.0.0+dfsg-2ubuntu1.47+esm6
  • qemu Ubuntu Pro 16.04 LTS 1:2.5+dfsg-5ubuntu10.51+esm4

ubuntu advisories UBUNTU-CVE-2021-20257

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • SLOF advanced virtualization 8.5 20210217-1.module+el8.5.0+10946+35bb3930
  • hivex advanced virtualization 8.5 1.3.18-22.module+el8.5.0+12087+2208d04c
  • netcf advanced virtualization 8.5 0.2.8-12.module+el8.4.0+8855+a9e237a9
  • swtpm advanced virtualization 8.5 0.6.0-2.20210607gitea627b3.module+el8.5.0+12696+4ce1c6bc
  • libnbd advanced virtualization 8.5 1.6.0-4.module+el8.5.0+11638+3d8f9850
  • nbdkit advanced virtualization 8.5 1.24.0-1.module+el8.4.0+9341+96cf2672
  • libtpms advanced virtualization 8.5 0.7.4-6.20201106git2452a24dab.module+el8.5.0+12487+f2fa92b4
  • libvirt advanced virtualization 8.5 7.6.0-6.module+el8.5.0+13051+7ddbe958

red hat advisories RHSA-2022:0081RHSA-2021:5238

  • xen SLES 12 SP2-BCL 4.7.6_22-43.88.1
  • qemu SLES for SAP 12 SP4, SLES 12 SP4-LTSS, OpenStack Cloud Crowbar 9 +1 more 2.11.2-5.32.1
  • qemu SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +7 more 3.1.1.1-9.27.2
  • qemu SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 2.11.2-9.46.1
  • qemu SLES for SAP 12 SP3, SLES 12 SP3-LTSS, SLES 12 SP3-BCL +3 more 2.9.1-6.50.1
  • qemu SLE Module for Server Applications 15 SP2, SLE Module for Basesystem 15 SP2, SLE Micro 5.0 4.2.1-11.19.2
  • qemu SLES for SAP 12 SP5, SLES 12 SP5 3.1.1.1-51.1
  • qemu SLES 12 SP2-BCL 2.6.2-41.65.1

suse advisories SUSE-SU-2022:1375-1SUSE-SU-2021:1947-1SUSE-SU-2021:1918-1SUSE-SU-2021:1895-1SUSE-SU-2021:1894-1SUSE-SU-2021:1893-1

  • qemu openSUSE Tumbleweed 6.1.0-32.1
  • qemu openSUSE Leap 15.2 4.2.1-lp152.9.16.2
  • qemu-testsuite openSUSE Leap 15.2 4.2.1-lp152.9.16.7
  • qemu-linux-user openSUSE Leap 15.2 4.2.1-lp152.9.16.1
  • qemu openSUSE Leap 15.2 4.2.1-lp152.9.12.1
  • qemu-testsuite openSUSE Leap 15.2 4.2.1-lp152.9.12.1
  • qemu-linux-user openSUSE Leap 15.2 4.2.1-lp152.9.12.1

opensuse advisories openSUSE-SU-2024:11287-1openSUSE-SU-2021:1043-1openSUSE-SU-2021:0600-1

  • hivex AlmaLinux 8 1.3.18-21.module_el8.5.0+2608+72063365
  • netcf AlmaLinux 8 0.2.8-12.module_el8.5.0+2608+72063365
  • netcf AlmaLinux 8 0.2.8-12.module_el8.6.0+2880+7d9e3703
  • libnbd AlmaLinux 8 1.2.2-1.module_el8.5.0+2608+72063365
  • nbdkit AlmaLinux 8 1.16.2-4.module_el8.5.0+2608+72063365
  • libvirt AlmaLinux 8 6.0.0-37.module_el8.5.0+2608+72063365
  • nbdfuse AlmaLinux 8 1.2.2-1.module_el8.5.0+2608+72063365
  • seabios AlmaLinux 8 1.13.0-2.module_el8.5.0+2608+72063365

almalinux advisories ALSA-2021:5238

  • hivex Rocky Linux 8 1.3.18-21.module+el8.4.0+642+7e26f5e1
  • hivex Rocky Linux 8 1.3.18-21.module+el8.5.0+670+c4aa478c
  • netcf Rocky Linux 8 0.2.8-12.module+el8.7.0+1084+97b81f61
  • netcf Rocky Linux 8 0.2.8-12.module+el8.4.0+534+4680a14e
  • netcf Rocky Linux 8 0.2.8-12.module+el8.6.0+847+b490afdd
  • libnbd Rocky Linux 8 1.2.2-1.module+el8.4.0+534+4680a14e
  • nbdkit Rocky Linux 8 1.16.2-4.module+el8.4.0+534+4680a14e
  • libvirt Rocky Linux 8 6.0.0-37.module+el8.5.0+670+c4aa478c

rocky linux advisories RLSA-2021:5238

  • qemu Alpine 3.15 6.1.1-r0

alpine advisories ALPINE-CVE-2021-20257

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • qemu CBL-Mariner 2.0 6.2.0-2

azure linux advisories AZL-9068

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-20257 updated cvss 3.2

QEMU: net: e1000: infinite loop while processing transmit descriptors

  • Red Hat Enterprise Linux 6 qemu-img, qemu-kvm, qemu-kvm-tools, qemu-guest-agent, qemu-guest-agent-win32
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 qemu-img, qemu-kvm, libcacard, qemu-kvm-rhev, qemu-kvm-tools, libcacard-tools, +2 more
    affected: no fix available “Fix deferred”
  • Red Hat Enterprise Linux 8 Advanced Virtualization qemu-img, qemu-kvm, qemu-kiwi, qemu-kvm-core, qemu-kvm-tests, qemu-kvm-common, +9 more
    affected: no fix available, no fix planned “Will not fix”
  • Red Hat OpenStack Platform 10 (Newton) qemu-img-rhev, qemu-kvm-rhev, qemu-kvm-tools-rhev, qemu-kvm-common-rhev Red Hat OpenStack Platform 13 (Queens) qemu-img-rhev, qemu-kvm-rhev, qemu-kvm-tools-rhev, qemu-kvm-common-rhev
    affected: no fix planned “Out of support scope”
  • Red Hat Advanced Virtualization for RHEL 8.5.0.Z netcf 0.2.8-12.module+el8.4.0+8855+a9e237a9, libnbd 1.6.0-4.module+el8.5.0+11638+3d8f9850, nbdkit 1.24.0-1.module+el8.4.0+9341+96cf2672, hivex 1.3.18-22.module+el8.5.0+12087+2208d04c, libvirt 7.6.0-6.module+el8.5.0+13051+7ddbe958, nbdfuse 1.6.0-4.module+el8.5.0+11638+3d8f9850, +110 more
    fixed: vendor fix RHSA-2022:0081
  • Red Hat CodeReady Linux Builder (v. 8) libnbd 1.2.2-1.module+el8.3.0+7353+9de0a3cc, netcf 0.2.8-12.module+el8.1.0+4066+0f1aadab, nbdfuse 1.2.2-1.module+el8.3.0+7353+9de0a3cc, hivex 1.3.18-21.module+el8.5.0+10709+b3edb581, seabios 1.13.0-2.module+el8.3.0+7353+9de0a3cc, libiscsi 1.18.0-8.module+el8.1.0+4066+0f1aadab, +39 more Red Hat Enterprise Linux AppStream (v. 8) libnbd 1.2.2-1.module+el8.3.0+7353+9de0a3cc, netcf 0.2.8-12.module+el8.1.0+4066+0f1aadab, nbdfuse 1.2.2-1.module+el8.3.0+7353+9de0a3cc, nbdkit 1.16.2-4.module+el8.3.0+6922+fd575af8, hivex 1.3.18-21.module+el8.5.0+10709+b3edb581, seabios 1.13.0-2.module+el8.3.0+7353+9de0a3cc, +88 more
    fixed: vendor fix RHSA-2021:5238
  • Red Hat Enterprise Linux 7 qemu-img-ma, qemu-kvm-ma, qemu-kvm-tools-ma, qemu-kvm-common-ma
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.37% chance of exploitation in the next 30 days, higher than 31% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
NVD 2.0 2.1 AV:L/AC:L/Au:N/C:N/I:N/A:P

Affected products

  • n/a QEMU

Classification

Weakness
  • CWE-835 Loop with Unreachable Exit Condition

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.