What is CVE-2021-0207?A high-severity flaw in Junos, explained.
CVE-2021-0207 is a high-severity flaw (CVSS 7.5) in Junos from Juniper, published on 15 January 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 1.3%. If you run an affected version, plan in the vendor’s fix.
Published 15 January 2021. Record last updated 5 February 2021. We keep this page's data up to date.
What is CVE-2021-0207? 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.
An improper interpretation conflict of certain data between certain software components within the Juniper Networks Junos OS devices does not allow certain traffic to pass through the device upon receipt from an ingress interface filtering certain specific types of traffic which is then being redirected to an egress interface on a different VLAN. This causes a Denial of Service (DoS) to those clients sending these particular types of traffic. Such traffic being sent by a client may appear genuine, but is non-standard in nature and should be considered as potentially malicious, and can be targeted to the device, or destined through it for the issue to occur. This issues affects IPv4 and IPv6 traffic. An indicator of compromise may be found by checking log files. You may find that traffic on the input interface has 100% of traffic flowing into the device, yet the egress interface shows 0 pps leaving the device. For example: [show interfaces "interface" statistics detail] Output between two interfaces would reveal something similar to: Ingress, first interface: -------------------- Interface Link Input packets (pps) Output packets (pps) et-0/0/0 Up 9999999999 (9999) 1 (0) -------------------- Egress, second interface: -------------------- Interface Link Input packets (pps) Output packets (pps) et-0/0/1 Up 0 (0) 9999999999 (0) -------------------- Dropped packets will not show up in DDoS monitoring/protection counters as issue is not caused by anti-DDoS protection mechanisms. This issue affects: Juniper Networks Junos OS: 17.3 versions prior to 17.3R3-S7 on NFX250, QFX5K Series, EX4600; 17.4 versions prior to 17.4R2-S11, 17.4R3-S3 on NFX250, QFX5K Series, EX4600; 18.1 versions prior to 18.1R3-S9 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4600; 18.2 versions prior to 18.2R3-S3 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600; 18.3 versions prior to 18.3R3-S1 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series; 18.4 versions prior to 18.4R1-S5, 18.4R2-S3, 18.4R3 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series; 19.1 versions prior to 19.1R1-S5, 19.1R2-S1, 19.1R3 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series; 19.2 versions prior to 19.2R1-S5, 19.2R2 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series; 19.3 versions prior to 19.3R2-S3, 19.3R3 on NFX250, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series; 19.4 versions prior to 19.4R1-S2, 19.4R2 on NFX250, NFX350, QFX5K Series, EX2300 Series, EX3400 Series, EX4300 Multigigabit, EX4600 Series. This issue does not affect Junos OS releases prior to 17.2R2.
What kind of flaw is it?
- CWE-115Misinterpretation of Input
- CWE-436Interpretation Conflict
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:U/C:N/I:N/A:H
Is CVE-2021-0207 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 1.3%. That can change at any time, which is why we keep watching.
Timeline
- Published
- Record last updated
CVE-2021-0207 scores 46. 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-2021-0207 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-2021-0207? 14 products.
The published record lists 14 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 versions17.317.3-r1-s117.3-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-s417.3-r3-s5 - Hardware
Ex2300
by Juniper
Affected versionsversion not specified - Hardware
Ex3400
by Juniper
Affected versionsversion not specified - Hardware
Ex4300
by Juniper
Affected versionsversion not specified - Hardware
Ex4600
by Juniper
Affected versionsversion not specified - Hardware
Nfx250
by Juniper
Affected versionsversion not specified - Hardware
Nfx350
by Juniper
Affected versionsversion not specified - Hardware
Qfx5100
by Juniper
Affected versionsversion not specified - Hardware
Qfx5110
by Juniper
Affected versionsversion not specified
How do I fix CVE-2021-0207? 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-2021-0207 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.
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1 new flaw affects software Acme tracks
An improper interpretation conflict of certain data between certain software components within the Juniper Networks Junos OS devices does not allow certain t...
- 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-2021-0207 is a high-severity flaw in Junos from Juniper, published on 15 January 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 7.5 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2021-0207 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.
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 1.3%. That can change at any time, which is why we keep watching.
For Junos from Juniper: 17.3, 17.3-r1-s1, 17.3-r2, 17.3-r2-s1, 17.3-r2-s2, 17.3-r2-s3 and 103 more. The record lists 14 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.