Skip to content
Fencer Vulns
low 3.8

CVE-2021-3594 json

An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU.

published 2021-06-15 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-26901

cvss
3.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 25%
public exploits
0
none known

Summary

An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU. The flaw exists in the udp_input() function and could occur while processing a udp packet that is smaller than the size of the 'udphdr' structure. This issue may lead to out-of-bounds read access or indirect host memory disclosure to the guest. The highest threat from this vulnerability is to data confidentiality. This flaw affects libslirp versions prior to 4.6.0.

Patch / fix

  • libslirp_project libslirp 4.6.0
  • qemu Debian 14, Debian 13, Debian 12 1:4.1-2
  • libslirp Debian 14, Debian 13, Debian 12 4.6.1-1

debian advisories DEBIAN-CVE-2021-3594

  • qemu Ubuntu 18.04 LTS 1:2.11+dfsg-1ubuntu7.37
  • libslirp Ubuntu 20.04 LTS 4.1.0-2ubuntu2.2
  • libslirp Ubuntu 22.04 LTS 4.6.1-1
  • qemu Ubuntu Pro 14.04 LTS 2.0.0+dfsg-2ubuntu1.47+esm4
  • qemu Ubuntu Pro 16.04 LTS 1:2.5+dfsg-5ubuntu10.51+esm3

ubuntu advisories UBUNTU-CVE-2021-3594

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 RHEL 8 20191022-3.git899d9883.module+el8.3.0+6423+e4cb6418
  • hivex RHEL 8 1.3.18-21.module+el8.5.0+10709+b3edb581
  • netcf RHEL 8 0.2.8-12.module+el8.1.0+4066+0f1aadab
  • libnbd RHEL 8 1.2.2-1.module+el8.3.0+7353+9de0a3cc
  • nbdkit RHEL 8 1.16.2-4.module+el8.3.0+6922+fd575af8
  • libvirt RHEL 8 6.0.0-37.module+el8.5.0+12162+40884dd2
  • nbdfuse RHEL 8 1.2.2-1.module+el8.3.0+7353+9de0a3cc
  • seabios RHEL 8 1.13.0-2.module+el8.3.0+7353+9de0a3cc

red hat advisories RHSA-2021:4191

  • libslirp SLE Module for Server Applications 15 SP4, SLE Module for Server Applications 15 SP3, SLE Micro 5.2 +3 more 4.3.1-150300.6.2
  • libslirp SLE Module for Server Applications 15 SP3, SLE Micro 5.2, SLE Micro 5.1 +2 more 4.3.1-150300.2.7.1
  • xen SLES 12 SP2-BCL 4.7.6_16-43.79.5
  • xen SLES for SAP 12 SP3, SLES 12 SP3-LTSS, SLES 12 SP3-BCL +3 more 4.9.4_20-3.91.1
  • xen SLES for SAP 12 SP4, SLES 12 SP4-LTSS, OpenStack Cloud Crowbar 9 +1 more 4.11.4_20-2.60.1
  • xen SLES for SAP 12 SP5, SLES 12 SP5, SLE Software Development Kit 12 SP5 4.12.4_12-3.49.1
  • kvm SLE Point of Sale 11 SP3 1.4.2-53.41.1
  • qemu SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +6 more 3.1.1.1-9.30.2

suse advisories SUSE-SU-2022:1730-1SUSE-SU-2022:1465-1SUSE-SU-2021:14848-1SUSE-SU-2021:3322-1SUSE-SU-2021:2957-1SUSE-SU-2021:2955-1

  • apr openSUSE Tumbleweed 1.7.0-2.2
  • libslirp openSUSE Tumbleweed 4.7.0+44-3.1
  • 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 3.1.1.1-9.30.2
  • qemu openSUSE Leap 15.3 4.2.1-11.25.2

opensuse advisories openSUSE-SU-2024:10628-1openSUSE-SU-2024:12529-1openSUSE-SU-2021:1202-1openSUSE-SU-2021:2591-1openSUSE-SU-2021:2474-1

  • 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-2021:4191

  • 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-2021:4191

  • libslirp Alpine 3.24, Alpine 3.23, Alpine 3.22 +8 more 4.6.0-r0

alpine advisories ALPINE-CVE-2021-3594

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

  • libslirp Arch Linux 4.6.0-1

arch linux advisories AVG-2073

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-2021-3594 updated cvss 3.8

QEMU: slirp: invalid pointer initialization may lead to information disclosure (udp)

  • 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: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 libslirp 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 “Fix deferred”
  • Red Hat Enterprise Linux 9 qemu-img, qemu-kvm, qemu-kvm-core, qemu-kvm-tools, qemu-pr-helper, qemu-kvm-common, +16 more
    affected: no fix available
  • 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 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-2021:4191
  • Red Hat Enterprise Linux 9 libslirp
    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

0.33% chance of exploitation in the next 30 days, higher than 25% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 3.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N
NVD 2.0 2.1 AV:L/AC:L/Au:N/C:P/I:N/A:N

Affected products

  • n/a QEMU

Classification

Weakness
  • CWE-824 Access of Uninitialized Pointer

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.