# What is CVE-2021-43784?

> CVE-2021-43784 is a medium-severity flaw (CVSS 5.0) in Runc from Linuxfoundation, published on 6 December 2021. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 1.8%. If you run an affected version, plan in the vendor’s fix.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-43784

## At a glance

- **Verdict:** Plan it in. No sign of exploitation and a low forecast. Patch it in your normal update cycle.
- **Precursor Intelligence risk score:** 43 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes.
- **Severity:** Medium (CVSS 5.0 out of 10)
- **Known to be exploited:** No, not on the list of flaws known to be exploited today
- **Chance of use in the next 30 days:** 1.8% (latest exploit-likelihood forecast)
- **Published:** 6 December 2021
- **Record last updated:** 19 February 2024
- **Main product:** Runc from Linuxfoundation
- **Affected products:** 2

## What is CVE-2021-43784? In plain terms

It can be attacked from anywhere on the internet with an ordinary user account, and nobody has to click anything. If it works, the attacker can read some data, change some data and slow it down.

### The 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.

### What kind of flaw is it?

- CWE-190: Integer Overflow or Wraparound

### How an attack on it works

- Where an attacker can be: Anywhere on the internet
- How hard it is to pull off: Hard: conditions must line up
- Login needed first: An ordinary user account
- Does someone have to click: No, nobody has to do anything
- What an attacker gets: Can read some data, change some data and slow it down

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

## Is CVE-2021-43784 being exploited? Not that we know of

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 1.8%. That can change at any time, which is why we keep watching.

Exploit likelihood over the last 7 days: 1.8%, 1.8%, 1.8%, 1.8%, 1.8%, 1.8%, 1.8%.

### Timeline

- 6 December 2021: Published
- 19 February 2024: Record last updated

### How Precursor Intelligence ranks it

CVE-2021-43784 scores **43 out of 100 (Medium)**, with the action "Plan remediation".

Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less:

- Evidence it is being exploited: biggest factor
- How severe it is: strong factor
- How widely exposed it is: smaller factor
- Threat activity around it: smaller factor

85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it.

## Who is affected by CVE-2021-43784?

The published record lists 2 products. Versions are as published: "before 1.0.3" means every version up to, but not including, 1.0.3.

- [Runc](https://www.precursorintelligence.com/product/linuxfoundation/runc) by [Linuxfoundation](https://www.precursorintelligence.com/vendors/linuxfoundation) (Application): before 1.0.3
- [Debian Linux](https://www.precursorintelligence.com/product/debian/debian_linux) by [Debian](https://www.precursorintelligence.com/vendors/debian) (Operating system): 9.0

## How do I fix CVE-2021-43784?

1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
2. **Apply the vendor’s fix.** Install the update named in the vendor’s advisory. We’ve put the advisories and patch notes first in the list.
3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
4. **Keep an eye on it.** Track the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood.

### References

- [github.com](https://github.com/opencontainers/runc/commit/9c444070ec7bb83995dbc0185da68284da71c554) (Patch, Third-party advisory)
- [github.com](https://github.com/opencontainers/runc/commit/d72d057ba794164c3cce9451a00b72a78b25e1ae) (Patch, Third-party advisory)
- [github.com](https://github.com/opencontainers/runc/commit/f50369af4b571e358f20b139eea52d612eb55eed) (Patch, Third-party advisory)
- [github.com](https://github.com/opencontainers/runc/security/advisories/GHSA-v95c-p5hm-xq8f) (Patch, Third-party advisory)
- [lists.debian.org](https://lists.debian.org/debian-lts-announce/2021/12/msg00005.html) (Vendor advisory)
- [bugs.chromium.org](https://bugs.chromium.org/p/project-zero/issues/detail?id=2241) (Exploit, Third-party advisory)
- [lists.debian.org](https://lists.debian.org/debian-lts-announce/2024/02/msg00005.html)

## Questions

### What is CVE-2021-43784?

CVE-2021-43784 is a medium-severity flaw in Runc from Linuxfoundation, published on 6 December 2021. It can be attacked from anywhere on the internet with an ordinary user account, and nobody has to click anything. If it works, the attacker can read some data, change some data and slow it down.

### How serious is CVE-2021-43784?

It scores 5.0 out of 10 on the CVSS severity scale, which is medium. Our risk score for CVE-2021-43784 is 43 out of 100, which is Medium. Its action is "Plan remediation". No sign of exploitation and a low forecast. Patch it in your normal update cycle.

### Is CVE-2021-43784 being exploited?

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 1.8%. That can change at any time, which is why we keep watching.

### Which versions does CVE-2021-43784 affect?

For Runc from Linuxfoundation: before 1.0.3. The record lists 2 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2021-43784?

Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet.

## Does CVE-2021-43784 affect you?

Precursor Intelligence keeps checking for you:

- **Tell us what you run.** Pick your software from a list, or let us work it out from your website.
- **We match it to every flaw.** Over 400,000 published flaws, checked against your list.
- **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it.
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