# What is CVE-2021-0251?

> CVE-2021-0251 is a high-severity flaw (CVSS 8.6) in Junos from Juniper, published on 22 April 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-2021-0251

## 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:** 47 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes.
- **Severity:** High (CVSS 8.6 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:** 22 April 2021
- **Record last updated:** 27 April 2021
- **Main product:** Junos from Juniper
- **Affected products:** 17

## What is CVE-2021-0251? 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

A NULL Pointer Dereference vulnerability in the Captive Portal Content Delivery (CPCD) services daemon (cpcd) of Juniper Networks Junos OS on MX Series with MS-PIC, MS-SPC3, MS-MIC or MS-MPC allows an attacker to send malformed HTTP packets to the device thereby causing a Denial of Service (DoS), crashing the Multiservices PIC Management Daemon (mspmand) process thereby denying users the ability to login, while concurrently impacting other mspmand services and traffic through the device. Continued receipt and processing of these malformed packets will create a sustained Denial of Service (DoS) condition. While the Services PIC is restarting, all PIC services will be bypassed until the Services PIC completes its boot process. An attacker sending these malformed HTTP packets to the device who is not part of the Captive Portal experience is not able to exploit this issue. This issue is not applicable to MX RE-based CPCD platforms. This issue affects: Juniper Networks Junos OS on MX Series 17.3 version 17.3R1 and later versions prior to 17.4 versions 17.4R2-S9, 17.4R3-S2; 18.1 versions prior to 18.1R3-S9; 18.2 versions prior to 18.2R3-S3; 18.3 versions prior to 18.3R3-S1; 18.4 versions prior to 18.4R3; 19.1 versions prior to 19.1R2-S2, 19.1R3; 19.2 versions prior to 19.2R2; 19.3 versions prior to 19.3R3. This issue does not affect: Juniper Networks Junos OS versions prior to 17.3R1.

### What kind of flaw is it?

- CWE-476: NULL Pointer Dereference

### 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:C/C:N/I:N/A:H`

## Is CVE-2021-0251 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

- 22 April 2021: Published
- 27 April 2021: Record last updated

### How Precursor Intelligence ranks it

CVE-2021-0251 scores **47 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-2021-0251?

The published record lists 17 products.

- [Junos](https://www.precursorintelligence.com/product/juniper/junos) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Operating system): 17.3-r1, 17.3-r1-s1, 17.3-r1-s4, 17.3-r2, 17.3-r2-s1, 17.3-r2-s2, 17.3-r2-s3, 17.3-r2-s4, 17.3-r2-s5, 17.3-r3, 17.3-r3-s1, 17.3-r3-s2, 17.3-r3-s3, 17.3-r3-s4, 17.3-r3-s5, 17.3-r3-s6, 17.3-r3-s7, 17.3-r3-s8, 17.3-r3-s9, 17.3-r3-s10, 17.4, 17.4-r1, 17.4-r1-s1, 17.4-r1-s2, 17.4-r1-s3, 17.4-r1-s4, 17.4-r1-s5, 17.4-r1-s6, 17.4-r1-s7, 17.4-r2, 17.4-r2-s1, 17.4-r2-s2, 17.4-r2-s3, 17.4-r2-s4, 17.4-r2-s5, 17.4-r2-s6, 17.4-r2-s7, 17.4-r2-s8, 17.4-r3, 17.4-r3-s1 and 87 more
- [Mx10](https://www.precursorintelligence.com/product/juniper/mx10) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx10003](https://www.precursorintelligence.com/product/juniper/mx10003) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx10008](https://www.precursorintelligence.com/product/juniper/mx10008) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx10016](https://www.precursorintelligence.com/product/juniper/mx10016) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx104](https://www.precursorintelligence.com/product/juniper/mx104) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx150](https://www.precursorintelligence.com/product/juniper/mx150) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx2008](https://www.precursorintelligence.com/product/juniper/mx2008) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx2010](https://www.precursorintelligence.com/product/juniper/mx2010) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx2020](https://www.precursorintelligence.com/product/juniper/mx2020) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx204](https://www.precursorintelligence.com/product/juniper/mx204) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx240](https://www.precursorintelligence.com/product/juniper/mx240) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx40](https://www.precursorintelligence.com/product/juniper/mx40) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx480](https://www.precursorintelligence.com/product/juniper/mx480) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx5](https://www.precursorintelligence.com/product/juniper/mx5) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx80](https://www.precursorintelligence.com/product/juniper/mx80) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified
- [Mx960](https://www.precursorintelligence.com/product/juniper/mx960) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified

## How do I fix CVE-2021-0251?

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/JSA11144) (Vendor advisory)

## Questions

### What is CVE-2021-0251?

CVE-2021-0251 is a high-severity flaw in Junos from Juniper, published on 22 April 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-2021-0251?

It scores 8.6 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2021-0251 is 47 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-2021-0251 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-2021-0251 affect?

For Junos from Juniper: 17.3-r1, 17.3-r1-s1, 17.3-r1-s4, 17.3-r2, 17.3-r2-s1, 17.3-r2-s2 and 121 more. The record lists 17 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2021-0251?

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-2021-0251 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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