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Fencer Vulns
high 8.5

CVE-2021-3682 json

A flaw was found in the USB redirector device emulation of QEMU in versions prior to 6.1.0-rc2.

published 2021-08-05 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-26972

cvss
8.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
2.9%
EPSS 2.9% chance of exploitation in 30 days, percentile 86%
public exploits
0
none known

Summary

A flaw was found in the USB redirector device emulation of QEMU in versions prior to 6.1.0-rc2. It occurs when dropping packets during a bulk transfer from a SPICE client due to the packet queue being full. A malicious SPICE client could use this flaw to make QEMU call free() with faked heap chunk metadata, resulting in a crash of QEMU or potential code execution with the privileges of the QEMU process on the host.

Patch / fix

  • qemu qemu 6.1.0
  • qemu Debian 14, Debian 13, Debian 12 1:6.0+dfsg-3

debian advisories DEBIAN-CVE-2021-3682

  • qemu Ubuntu 18.04 LTS 1:2.11+dfsg-1ubuntu7.39
  • qemu Ubuntu 20.04 LTS 1:4.2-3ubuntu6.21
  • qemu Ubuntu 22.04 LTS 1:6.2+dfsg-2ubuntu5
  • qemu Ubuntu Pro 14.04 LTS 2.0.0+dfsg-2ubuntu1.47+esm2
  • qemu Ubuntu Pro 16.04 LTS 1:2.5+dfsg-5ubuntu10.51+esm1

ubuntu advisories UBUNTU-CVE-2021-3682

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 8.4 20200717-1.gite18ddad8.module+el8.4.0+8855+a9e237a9
  • hivex advanced virtualization 8.4 1.3.18-21.module+el8.4.0+11609+2eba841a
  • netcf advanced virtualization 8.4 0.2.8-12.module+el8.4.0+8855+a9e237a9
  • swtpm advanced virtualization 8.4 0.4.2-1.20201201git2df14e3.module+el8.4.0+9341+96cf2672
  • libnbd advanced virtualization 8.4 1.6.0-3.module+el8.4.0+9856+bbc47853
  • nbdkit advanced virtualization 8.4 1.24.0-1.module+el8.4.0+9341+96cf2672
  • libtpms advanced virtualization 8.4 0.7.4-4.20201106git2452a24dab.module+el8.4.0+10596+32ba7df3
  • libvirt advanced virtualization 8.4 7.0.0-14.4.module+el8.4.0+12413+d23780e6

red hat advisories RHSA-2021:3703RHSA-2021:3704

  • qemu SLES for SAP 12 SP4, SLES 12 SP4-LTSS, OpenStack Cloud Crowbar 9 +1 more 2.11.2-5.40.2
  • qemu SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +3 more 3.1.1.1-80.40.1
  • qemu SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 2.11.2-70.59.1
  • qemu SLES 12 SP2-BCL 2.6.2-41.73.1
  • qemu SLE Module for Server Applications 15 SP3, SLE Module for Basesystem 15 SP3 5.2.0-103.2
  • qemu SLES for SAP 12 SP5, SLES 12 SP5 3.1.1.1-57.2
  • qemu SLE Module for Server Applications 15 SP2, SLE Module for Basesystem 15 SP2, SLE Micro 5.0 4.2.1-11.28.1
  • xen SLES 11 SP4-LTSS 4.4.4_50-61.67.1

suse advisories SUSE-SU-2021:14848-1SUSE-SU-2021:3635-1SUSE-SU-2021:3614-1SUSE-SU-2021:3613-1SUSE-SU-2021:3575-1SUSE-SU-2021:2858-1

  • qemu openSUSE Tumbleweed 6.1.0-32.1
  • qemu openSUSE Leap 15.3 3.1.1.1-80.40.1
  • qemu openSUSE Leap 15.3 5.2.0-103.2
  • qemu openSUSE Leap 15.2 4.2.1-lp152.9.20.1
  • qemu-testsuite openSUSE Leap 15.2 4.2.1-lp152.9.20.1
  • qemu-linux-user openSUSE Leap 15.2 4.2.1-lp152.9.20.1
  • qemu openSUSE Leap 15.3 4.2.1-11.28.1

opensuse advisories openSUSE-SU-2024:11287-1openSUSE-SU-2021:3614-1openSUSE-SU-2021:2858-1openSUSE-SU-2021:1202-1openSUSE-SU-2021:2789-1

  • SLOF AlmaLinux 8 20210217-1.module_el8.6.0+2880+7d9e3703
  • hivex AlmaLinux 8 1.3.18-23.module_el8.6.0+2880+7d9e3703
  • netcf AlmaLinux 8 0.2.8-12.module_el8.6.0+2880+7d9e3703
  • swtpm AlmaLinux 8 0.7.0-1.20211109gitb79fd91.module_el8.6.0+2880+7d9e3703
  • libnbd AlmaLinux 8 1.6.0-5.module_el8.6.0+2880+7d9e3703
  • nbdkit AlmaLinux 8 1.24.0-4.module_el8.6.0+2880+7d9e3703
  • libtpms AlmaLinux 8 0.9.1-0.20211126git1ff6fe1f43.module_el8.6.0+2880+7d9e3703
  • libvirt AlmaLinux 8 8.0.0-5.module_el8.6.0+2880+7d9e3703

almalinux advisories ALSA-2022:1759

  • qemu Alpine 3.24, Alpine 3.23, Alpine 3.22 +6 more 6.1.0-r0

alpine advisories ALPINE-CVE-2021-3682

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-6830

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-2021-3682 updated cvss 8.5

QEMU: usbredir: free() call on invalid pointer in bufp_alloc()

  • Red Hat Enterprise Linux 6 qemu-img, qemu-kvm, qemu-kvm-tools, qemu-guest-agent, qemu-guest-agent-win32 Red Hat Enterprise Linux 7 qemu-img, qemu-kvm, libcacard, qemu-img-ma, qemu-kvm-ma, qemu-kvm-rhev, +6 more
    affected: workaround, no fix planned “Out of support scope”
  • 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: workaround, 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: workaround, no fix planned “Out of support scope”
  • Red Hat Advanced Virtualization CodeReady Builder for RHEL 8.2.1 libnbd 1.2.2-1.module+el8.2.0+5644+32ac38d4, netcf 0.2.8-12.module+el8.2.0+4793+b09dd2fb, hivex 1.3.18-20.module+el8.2.0+5588+63a201c3, nbdfuse 1.2.2-1.module+el8.2.0+5644+32ac38d4, seabios 1.13.0-2.module+el8.2.1+7284+aa32a2c4, libiscsi 1.18.0-8.module+el8.2.0+4793+b09dd2fb, +45 more Red Hat Advanced Virtualization for RHEL 8.2.1 libnbd 1.2.2-1.module+el8.2.0+5644+32ac38d4, netcf 0.2.8-12.module+el8.2.0+4793+b09dd2fb, hivex 1.3.18-20.module+el8.2.0+5588+63a201c3, nbdfuse 1.2.2-1.module+el8.2.0+5644+32ac38d4, nbdkit 1.16.2-4.module+el8.2.1+6710+effcb1df, seabios 1.13.0-2.module+el8.2.1+7284+aa32a2c4, +96 more
    fixed: vendor fix RHSA-2021:3704
  • Red Hat Advanced Virtualization for RHEL 8.4.0.Z libnbd 1.6.0-3.module+el8.4.0+9856+bbc47853, netcf 0.2.8-12.module+el8.4.0+8855+a9e237a9, nbdfuse 1.6.0-3.module+el8.4.0+9856+bbc47853, nbdkit 1.24.0-1.module+el8.4.0+9341+96cf2672, hivex 1.3.18-21.module+el8.4.0+11609+2eba841a, seabios 1.14.0-1.module+el8.4.0+8855+a9e237a9, +110 more
    fixed: vendor fix RHSA-2021:3703
  • Red Hat Enterprise Linux AppStream (v. 8) libnbd 1.6.0-5.module+el8.6.0+14480+c0a3aa0f, netcf 0.2.8-12.module+el8.6.0+14480+c0a3aa0f, hivex 1.3.18-23.module+el8.6.0+14480+c0a3aa0f, libvirt 8.0.0-5.module+el8.6.0+14480+c0a3aa0f, nbdfuse 1.6.0-5.module+el8.6.0+14480+c0a3aa0f, nbdkit 1.24.0-4.module+el8.6.0+14480+c0a3aa0f, +104 more Red Hat Enterprise Linux CRB (v. 8) libnbd 1.6.0-5.module+el8.6.0+14480+c0a3aa0f, netcf 0.2.8-12.module+el8.6.0+14480+c0a3aa0f, hivex 1.3.18-23.module+el8.6.0+14480+c0a3aa0f, libvirt 8.0.0-5.module+el8.6.0+14480+c0a3aa0f, nbdfuse 1.6.0-5.module+el8.6.0+14480+c0a3aa0f, SLOF 20210217-1.module+el8.6.0+14480+c0a3aa0f, +38 more
    fixed: vendor fix RHSA-2022:1759
  • Red Hat Enterprise Linux 9 qemu-img, qemu-kvm, qemu-kvm-core, qemu-kvm-tools, qemu-pr-helper, qemu-kvm-common, +16 more
    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

2.88% chance of exploitation in the next 30 days, higher than 86% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 8.5 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
NVD 2.0 6.0 AV:N/AC:M/Au:S/C:P/I:P/A:P

Affected products

  • n/a QEMU

Classification

Weakness
  • CWE-763 Release of Invalid Pointer or Reference

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.