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MEDIUM

CVE-2021-43784

CVSS v3

5

MEDIUM

EPSS Score

1.8 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • github.com/opencontainers/runcGofrom 1.0.1-0.20211012131345-9c444070ec7b · fixed in 1.1.0
  • runcAlmaLinux:9all versions · fixed in 4:1.1.9-1.el9

Vendor advisories

  • CVE-2021-43784 Red Hat Product Security13 products fixed · 8 known affected

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

    runc.src (container-tools:2.0) as a component of Red Hat Enterprise Linux 8 · runc.src (container-tools:3.0) as a component of Red Hat Enterprise Linux 8 · runc.src (container-tools:rhel8) as a component of Red Hat Enterprise Linux 8

  • RHSA-2023:6380 Red Hat Product Security13 products fixed

    Red Hat Security Advisory: runc security update

Full record on NVD

Description

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.

Technical details

Published
2021-12-06

Frequently asked questions

What is CVE-2021-43784?

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.

Is CVE-2021-43784 actively exploited?

Active exploitation of CVE-2021-43784 has not been confirmed. Its EPSS score was 1.8% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-43784?

CVE-2021-43784 has a CVSS v3 base score of 5 (MEDIUM severity).

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