# CVE-2021-43784: Overflow in netlink bytemsg length field allows attacker to override netlink-based container configuration > An integer overflow in runc allows attackers with container configuration control to bypass namespace restrictions and escape the container. - **Severity:** Medium 6.0 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:L/A:L`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 6 Dec 2021 - **Updated:** 15 Oct 2024 - **Also known as:** AZL-6682, CLEANSTART-2026-DZ88951, DEBIAN-CVE-2021-43784, DLA-2841-1, GHSA-v95c-p5hm-xq8f, GO-2022-0274, MGASA-2021-0553, SUSE-SU-2021:4059-1, SUSE-SU-2021:4171-1, UBUNTU-CVE-2021-43784, openSUSE-SU-2021:1625-1, openSUSE-SU-2021:4171-1, openSUSE-SU-2024:11664-1 ## What is CVE-2021-43784? CVE-2021-43784 is a medium-severity vulnerability in Debian Debian Linux, published on 6 Dec 2021. Any signed-in user can exploit it over the network, with no action from the victim. ### Official 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. Weakness: CWE-190 (Integer Overflow or Wraparound) ## Which versions are affected by CVE-2021-43784? 3 open source packages ship an affected version, including github.com/opencontainers/runc. It affects 2 products. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `github.com/opencontainers/runc` | Go | All versions | 1.0.3 | | `github.com/opencontainers/runc` | Go | All versions | 1.0.3 | | `github.com/opencontainers/runc` | Go | From 1.0.1-0.20211012131345-9c444070ec7b | 1.1.0 | | `runc` | SUSE:Enterprise Storage 7 | All versions | 1.0.3-27.1 | | `runc` | SUSE:Linux Enterprise Micro 5.0 | All versions | 1.0.3-27.1 | | `runc` | SUSE:Linux Enterprise Micro 5.1 | All versions | 1.0.3-27.1 | | `runc` | SUSE:Linux Enterprise Module for Containers 12 | All versions | 1.0.3-16.18.1 | | `runc` | SUSE:Linux Enterprise Module for Containers 15 SP2 | All versions | 1.0.3-27.1 | | `runc` | SUSE:Linux Enterprise Module for Containers 15 SP3 | All versions | 1.0.3-27.1 | | `runc` | openSUSE:Leap 15.2 | All versions | 1.0.3-lp152.2.12.1 | | `runc` | openSUSE:Leap 15.3 | All versions | 1.0.3-27.1 | | `runc` | openSUSE:Tumbleweed | All versions | 1.0.3-1.1 | Products: Debian Debian Linux, Linuxfoundation Runc. ## How do I fix CVE-2021-43784? Upgrade github.com/opencontainers/runc to a fixed version for your release line: 1.0.3 or 1.1.0. ## Is CVE-2021-43784 being exploited? There is no known exploitation of CVE-2021-43784 in the wild and no public exploit code. ## Other vulnerabilities in Debian Debian Linux - [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild) - [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild) - [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild) - [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild) - [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2021-43784 and fix it if it is affected. What it is: CVE-2021-43784 is a medium-severity vulnerability in Debian Debian Linux, published on 6 Dec 2021. Any signed-in user can exploit it over the network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2021-43784 in the wild and no public exploit code. Affected packages and fixed versions: - github.com/opencontainers/runc (Go): affected all versions; fixed in 1.0.3 - github.com/opencontainers/runc (Go): affected all versions; fixed in 1.0.3 - github.com/opencontainers/runc (Go): affected from 1.0.1-0.20211012131345-9c444070ec7b; fixed in 1.1.0 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2021-43784/ (Markdown: https://insights.sbomify.com/CVE-2021-43784/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-43784 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-43784 - OSV: https://osv.dev/vulnerability/CVE-2021-43784 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-43784/ Summaries are generated and may contain mistakes; the official description above is the record.