# What is CVE-2021-31368?

> CVE-2021-31368 is a high-severity flaw (CVSS 7.5) in Junos from Juniper, published on 19 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 1.1%. If you run an affected version, plan in the vendor’s fix.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-31368

## 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:** 46 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes.
- **Severity:** High (CVSS 7.5 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:** 1.1% (latest exploit-likelihood forecast)
- **Published:** 19 October 2021
- **Record last updated:** 26 October 2021
- **Main product:** Junos from Juniper
- **Affected products:** 6

## What is CVE-2021-31368? In plain terms

It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can take it offline.

### The official description

An Uncontrolled Resource Consumption vulnerability in the kernel of Juniper Networks JUNOS OS allows an unauthenticated network based attacker to cause 100% CPU load and the device to become unresponsive by sending a flood of traffic to the out-of-band management ethernet port. Continued receipted of a flood will create a sustained Denial of Service (DoS) condition. Once the flood subsides the system will recover by itself. An indication that the system is affected by this issue would be that kernel and netisr process are shown to be using a lot of CPU cycles like in the following example output: user@host> show system processes extensive ... PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU COMMAND 16 root -72 - 0K 304K WAIT 1 839:40 88.96% intr{swi1: netisr 0} 0 root 97 - 0K 160K RUN 1 732:43 87.99% kernel{bcm560xgmac0 que} This issue affects Juniper Networks JUNOS OS on EX2300 Series, EX3400 Series, and ACX710: All versions prior to 18.1R3-S13; 18.2 versions prior to 18.2R3-S8; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R2-S8, 18.4R3-S9; 19.1 versions prior to 19.1R3-S5; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R1-S4, 19.4R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3; 20.2 versions prior to 20.2R3; 20.3 versions prior to 20.3R2-S1, 20.3R3; 20.4 versions prior to 20.4R2.

### What kind of flaw is it?

- CWE-400: Uncontrolled Resource Consumption

### How an attack on it works

- Where an attacker can be: Anywhere on the internet
- How hard it is to pull off: Easy: no special conditions
- Login needed first: No login needed
- Does someone have to click: No, nobody has to do anything
- What an attacker gets: Can take it offline

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

## Is CVE-2021-31368 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 1.1%. That can change at any time, which is why we keep watching.

Exploit likelihood over the last 7 days: 1.1%, 1.1%, 1.1%, 1.1%, 1.1%, 1.1%, 1.1%.

### Timeline

- 19 October 2021: Published
- 26 October 2021: Record last updated

### How Precursor Intelligence ranks it

CVE-2021-31368 scores **46 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-2021-31368?

The published record lists 6 products. Versions are as published: "before 18.1" means every version up to, but not including, 18.1.

- [Junos](https://www.precursorintelligence.com/product/juniper/junos) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Operating system): before 18.1, 18.1, 18.1-r, 18.1-r1, 18.1-r2, 18.1-r2-s1, 18.1-r2-s2, 18.1-r2-s4, 18.1-r3, 18.1-r3-s1, 18.1-r3-s2, 18.1-r3-s3, 18.1-r3-s4, 18.1-r3-s5, 18.1-r3-s6, 18.1-r3-s7, 18.1-r3-s8, 18.1-r3-s9, 18.1-r3-s10, 18.1-r3-s11, 18.1-r3-s12, 18.2, 18.2-r, 18.2-r1, 18.2-r1-s2, 18.2-r1-s3, 18.2-r1-s4, 18.2-r1-s5, 18.2-r2, 18.2-r2-s1, 18.2-r2-s2, 18.2-r2-s3, 18.2-r2-s4, 18.2-r2-s5, 18.2-r2-s6, 18.2-r2-s7, 18.2-r2-s8, 18.2-r3, 18.2-r3-s1, 18.2-r3-s2 and 124 more
- [Acx710](https://www.precursorintelligence.com/product/juniper/acx710) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Ex2300](https://www.precursorintelligence.com/product/juniper/ex2300) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Ex2300-C](https://www.precursorintelligence.com/product/juniper/ex2300-c) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Ex2300m](https://www.precursorintelligence.com/product/juniper/ex2300m) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Ex3400](https://www.precursorintelligence.com/product/juniper/ex3400) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified

## How do I fix CVE-2021-31368?

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

- [kb.juniper.net](https://kb.juniper.net/JSA11230) (Vendor advisory)

## Questions

### What is CVE-2021-31368?

CVE-2021-31368 is a high-severity flaw in Junos from Juniper, published on 19 October 2021. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can take it offline.

### How serious is CVE-2021-31368?

It scores 7.5 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2021-31368 is 46 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-2021-31368 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 1.1%. That can change at any time, which is why we keep watching.

### Which versions does CVE-2021-31368 affect?

For Junos from Juniper: before 18.1, 18.1, 18.1-r, 18.1-r1, 18.1-r2, 18.1-r2-s1 and 158 more. The record lists 6 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2021-31368?

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-2021-31368 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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