What is CVE-2021-0251?A high-severity flaw in Junos, explained.
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.
Published 22 April 2021. Record last updated 27 April 2021. We keep this page's data up to date.
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.
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-476NULL Pointer Dereference
How an attack on it works
Read straight from its severity rating, translated out of the shorthand.
- Where an attacker can beAnywhere on the internet
- How hard it is to pull offEasy: no special conditions
- Login needed firstNo login needed
- Does someone have to clickNo, nobody has to do anything
- What an attacker getsCan 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.
Timeline
- Published
- Record last updated
CVE-2021-0251 scores 47. Action: Plan remediation.
We keep the score of every published flaw up to date as the evidence changes. Four things go into the score, and evidence that criminals are actually using it counts most. In order:
- Evidence it is being exploitedBiggest factor
- How severe it isStrong factor
- How widely exposed it isSmaller factor
- Threat activity around itSmaller factor
85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score.
When CVE-2021-0251 matches software you track, it lands in your list with its score and the reasons behind it.
See your own ranked list →Who is affected by CVE-2021-0251? 17 products.
The published record lists 17 products from 1 vendor. If you run one of these, check your version, then go to the fix below.
- Operating system
Junos
by Juniper
Affected versions17.3-r117.3-r1-s117.3-r1-s417.3-r217.3-r2-s117.3-r2-s217.3-r2-s317.3-r2-s417.3-r2-s517.3-r317.3-r3-s117.3-r3-s217.3-r3-s317.3-r3-s4 - Hardware
Mx10
by Juniper
Affected versionsversion not specified - Hardware
Mx10003
by Juniper
Affected versionsversion not specified - Hardware
Mx10008
by Juniper
Affected versionsversion not specified - Hardware
Mx10016
by Juniper
Affected versionsversion not specified - Hardware
Mx104
by Juniper
Affected versionsversion not specified - Hardware
Mx150
by Juniper
Affected versionsversion not specified - Hardware
Mx2008
by Juniper
Affected versionsversion not specified - Hardware
Mx2010
by Juniper
Affected versionsversion not specified
How do I fix CVE-2021-0251? Four steps.
- Check whether you run itCompare 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.
- Apply the vendor’s fixInstall the update named in the vendor’s advisory. We’ve put the advisory first in the list.
- If you can’t patch todayFollow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
- Keep an eye on itTrack 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
1 linkDoes CVE-2021-0251 affect you? We'll keep checking.
Looking flaws up one at a time doesn't scale. Tell us what you run once, and we tell you which flaws matter to you, in what order, and keep watching for new ones.
- Tell us what you runPick your software from a list, or let us work it out from your website.
- We match it to every flawOver 400,000 published flaws, checked against your list.
- Ranked by real-world riskA 0 to 100 score, led by evidence criminals are using it.
- Told as soon as we knowAn alert by email, in the app or by webhook to your own tools.
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1 new flaw affects software Acme tracks
A NULL Pointer Dereference vulnerability in the Captive Portal Content Delivery (CPCD) services daemon (cpcd) of Juniper Networks Junos OS on MX Series with ...
- Matched to
- Junos on Acme's software list
- What to do
- Plan in the vendor’s update
Sent to the alert recipients Acme chose. Also in the app and to Acme's webhook.
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.
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.
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.
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.
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.