# What is CVE-2021-41091?

> CVE-2021-41091 is a medium-severity flaw (CVSS 6.3) in Moby from Mobyproject, published on 4 October 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 2.8%. If you run an affected version, plan in the vendor’s fix.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-41091

## 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:** 44 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes.
- **Severity:** Medium (CVSS 6.3 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:** 2.8% (latest exploit-likelihood forecast)
- **Published:** 4 October 2021
- **Record last updated:** 7 November 2023
- **Main product:** Moby from Mobyproject
- **Affected products:** 2

## What is CVE-2021-41091? In plain terms

An attacker has to be already on the device 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

Moby is an open-source project created by Docker to enable software containerization. A bug was found in Moby (Docker Engine) where the data directory (typically `/var/lib/docker`) contained subdirectories with insufficiently restricted permissions, allowing otherwise unprivileged Linux users to traverse directory contents and execute programs. When containers included executable programs with extended permission bits (such as `setuid`), unprivileged Linux users could discover and execute those programs. When the UID of an unprivileged Linux user on the host collided with the file owner or group inside a container, the unprivileged Linux user on the host could discover, read, and modify those files. This bug has been fixed in Moby (Docker Engine) 20.10.9. Users should update to this version as soon as possible. Running containers should be stopped and restarted for the permissions to be fixed. For users unable to upgrade limit access to the host to trusted users. Limit access to host volumes to trusted containers.

### What kind of flaw is it?

- CWE-732: Incorrect Permission Assignment for Critical Resource
- CWE-281: Improper Preservation of Permissions

### How an attack on it works

- Where an attacker can be: Already on the device
- How hard it is to pull off: Easy: no special conditions
- 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:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:L`

## Is CVE-2021-41091 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 2.8%. That can change at any time, which is why we keep watching.

Exploit likelihood over the last 7 days: 2.8%, 2.8%, 2.8%, 2.8%, 2.8%, 2.8%, 2.8%.

### Timeline

- 4 October 2021: Published
- 7 November 2023: Record last updated

### How Precursor Intelligence ranks it

CVE-2021-41091 scores **44 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-2021-41091?

The published record lists 2 products. Versions are as published: "before 20.10.9" means every version up to, but not including, 20.10.9.

- [Moby](https://www.precursorintelligence.com/product/mobyproject/moby) by [Mobyproject](https://www.precursorintelligence.com/vendors/mobyproject) (Application): before 20.10.9
- [Fedora](https://www.precursorintelligence.com/product/fedoraproject/fedora) by [Fedoraproject](https://www.precursorintelligence.com/vendors/fedoraproject) (Operating system): 34, 35

## How do I fix CVE-2021-41091?

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 advisory 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/moby/moby/commit/f0ab919f518c47240ea0e72d0999576bb8008e64) (Patch, Third-party advisory)
- [cert-portal.siemens.com](https://cert-portal.siemens.com/productcert/pdf/ssa-222547.pdf)
- [github.com](https://github.com/moby/moby/security/advisories/GHSA-3fwx-pjgw-3558) (Third-party advisory)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/B5Q6G6I4W5COQE25QMC7FJY3I3PAYFBB/)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZNFADTCHHYWVM6W4NJ6CB4FNFM2VMBIB/)

## Questions

### What is CVE-2021-41091?

CVE-2021-41091 is a medium-severity flaw in Moby from Mobyproject, published on 4 October 2021. An attacker has to be already on the device 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-2021-41091?

It scores 6.3 out of 10 on the CVSS severity scale, which is medium. Our risk score for CVE-2021-41091 is 44 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-2021-41091 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 2.8%. That can change at any time, which is why we keep watching.

### Which versions does CVE-2021-41091 affect?

For Moby from Mobyproject: before 20.10.9. The record lists 2 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2021-41091?

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-2021-41091 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.
- **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools.

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