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 serializa...

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.

Metrics

CVSS 3.1

5/10

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L

EPSS Probability

1.66%

73.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-190

Affected Software

Vendor	Product	Versions
Linuxfoundation	Runc	< 1.0.3
Debian	Debian Linux	9.0

References

https://bugs.chromium.org/p/project-zero/issues/detail?id=2241Exploit, Third Party Advisory
https://github.com/opencontainers/runc/commit/9c444070ec7bb83995dbc0185da68284da71c554Patch, Third Party Advisory
https://github.com/opencontainers/runc/commit/d72d057ba794164c3cce9451a00b72a78b25e1aePatch, Third Party Advisory
https://github.com/opencontainers/runc/commit/f50369af4b571e358f20b139eea52d612eb55eedPatch, Third Party Advisory
https://github.com/opencontainers/runc/security/advisories/GHSA-v95c-p5hm-xq8fPatch, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2021/12/msg00005.htmlVendor Advisory
https://lists.debian.org/debian-lts-announce/2024/02/msg00005.html
https://bugs.chromium.org/p/project-zero/issues/detail?id=2241Exploit, Third Party Advisory
https://github.com/opencontainers/runc/commit/9c444070ec7bb83995dbc0185da68284da71c554Patch, Third Party Advisory
https://github.com/opencontainers/runc/commit/d72d057ba794164c3cce9451a00b72a78b25e1aePatch, Third Party Advisory
https://github.com/opencontainers/runc/commit/f50369af4b571e358f20b139eea52d612eb55eedPatch, Third Party Advisory
https://github.com/opencontainers/runc/security/advisories/GHSA-v95c-p5hm-xq8fPatch, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2021/12/msg00005.htmlVendor Advisory
https://lists.debian.org/debian-lts-announce/2024/02/msg00005.html

Timeline

Published: Dec 6, 2021
Last Modified: Jun 17, 2026
Status: Modified

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.

How severe is CVE-2021-43784?

CVE-2021-43784 has a CVSS score of 5/10 (MEDIUM severity). The EPSS model estimates a 1.66% probability of exploitation in the next 30 days.

How do I fix CVE-2021-43784?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.