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Fencer Vulns
medium 6.0

CVE-2021-43784 json

Overflow in netlink bytemsg length field allows attacker to override netlink-based container configuration

published 2021-12-06 4 y ago modified 2026-09-10 1 mo ago also GHSA-v95c-p5hm-xq8f , GO-2022-0274 , EUVD-2021-2591

cvss
6.0
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.8%
EPSS 1.8% chance of exploitation in 30 days, percentile 78%
public exploits
0
none known

Summary

runc is a CLI tool for spawning and running containers on Linux according to the OCI specification. In runc, netlink is used internally as a serialization system for specifying the relevant container configuration to the `C` portion of the code (responsible for the based namespace setup of containers). In all versions of runc prior to 1.0.3, the encoder did not handle the possibility of an integer overflow in the 16-bit length field for the byte array attribute type, meaning that a large enough malicious byte array attribute could result in the length overflowing and the attribute contents being parsed as netlink messages for container configuration. This vulnerability requires the attacker to have some control over the configuration of the container and would allow the attacker to bypass the namespace restrictions of the container by simply adding their own netlink payload which disables all namespaces. The main users impacted are those who allow untrusted images with untrusted configurations to run on their machines (such as with shared cloud infrastructure). runc version 1.0.3 contains a fix for this bug. As a workaround, one may try disallowing untrusted namespace paths from your container. It should be noted that untrusted namespace paths would allow the attacker to disable namespace protections entirely even in the absence of this bug.

Patch / fix

  • go github.com/opencontainers/runc 1.0.3, 1.1.0
  • linuxfoundation runc 1.0.3
  • runc Debian 14, Debian 13, Debian 12 1.0.3+ds1-1

debian advisories DEBIAN-CVE-2021-43784

  • runc Ubuntu Pro 16.04 LTS 1.0.0~rc7+git20190403.029124da-0ubuntu1~16.04.4+esm4

ubuntu advisories UBUNTU-CVE-2021-43784

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

  • runc RHEL 9 4:1.1.9-1.el9

red hat advisories RHSA-2023:6380

  • runc SLE Module for Containers 15 SP3, SLE Module for Containers 15 SP2, SLE Micro 5.1 +2 more 1.0.3-27.1
  • runc SLE Module for Containers 12 1.0.3-16.18.1

suse advisories SUSE-SU-2021:4171-1SUSE-SU-2021:4059-1

  • runc openSUSE Tumbleweed 1.0.3-1.1
  • runc openSUSE Leap 15.2 1.0.3-lp152.2.12.1
  • runc openSUSE Leap 15.3 1.0.3-27.1

opensuse advisories openSUSE-SU-2024:11664-1openSUSE-SU-2021:1625-1openSUSE-SU-2021:4171-1

  • runc AlmaLinux 9 4:1.1.9-1.el9

almalinux advisories ALSA-2023:6380

  • runc Alpine 3.24, Alpine 3.23, Alpine 3.22 +7 more 1.0.3-r0

alpine advisories ALPINE-CVE-2021-43784

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

  • moby-runc CBL-Mariner 2.0 1.1.0-1

azure linux advisories AZL-6682

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

  • runc Arch Linux 1.0.3-1

arch linux advisories AVG-2599

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-2021-43784 updated cvss 5.0

runc: integer overflow in netlink bytemsg length field allows attacker to override netlink-based container configuration

  • Red Hat Enterprise Linux 8 runc
    affected: no fix available “Fix deferred”
  • Red Hat OpenShift Container Platform 3.11 runc
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 9) runc 1.1.9-1.el9
    fixed: vendor fix RHSA-2023:6380
  • Red Hat OpenShift Container Platform 4 runc
    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

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

1.80% chance of exploitation in the next 30 days, higher than 78% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugs.chromium.org https://bugs.chromium.org/p/project-zero/issues/detail?id=2241 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 6.0 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:L/A:L
NVD 3.1 5.0 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L
NVD 2.0 6.0 AV:N/AC:M/Au:S/C:P/I:P/A:P
GitHub 3.1 6.0 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:L/A:L

Affected packages

ecosystem package affected fixed in
go github.com/opencontainers/runc
<1.0.3
>=1.0.1-0.20211012131345-9c444070ec7b, <1.1.0
1.0.3
1.1.0

Affected products

  • opencontainers runc

Classification

Weakness
  • CWE-190 Integer Overflow or Wraparound

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.