# What is CVE-2021-0207? > 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. Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-0207 ## 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:** 1.3% (latest exploit-likelihood forecast) - **Published:** 15 January 2021 - **Record last updated:** 5 February 2021 - **Main product:** Junos from Juniper - **Affected products:** 14 ## 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. ### The official description 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-436: Interpretation Conflict - CWE-115: Misinterpretation of Input ### 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-2021-0207 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. Exploit likelihood over the last 7 days: 1.3%, 1.3%, 1.3%, 1.3%, 1.3%, 1.3%, 1.3%. ### Timeline - 15 January 2021: Published - 5 February 2021: Record last updated ### How Precursor Intelligence ranks it CVE-2021-0207 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-2021-0207? The published record lists 14 products. - [Junos](https://www.precursorintelligence.com/product/juniper/junos) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Operating system): 17.3, 17.3-r1-s1, 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, 17.4, 17.4-r1, 17.4-r1-s1, 17.4-r1-s2, 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-r2-s9, 17.4-r2-s10, 17.4-r3, 17.4-r3-s1, 17.4-r3-s2, 18.1, 18.1-r1, 18.1-r2 and 69 more - [Ex2300](https://www.precursorintelligence.com/product/juniper/ex2300) 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 - [Ex4300](https://www.precursorintelligence.com/product/juniper/ex4300) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified - [Ex4600](https://www.precursorintelligence.com/product/juniper/ex4600) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified - [Nfx250](https://www.precursorintelligence.com/product/juniper/nfx250) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified - [Nfx350](https://www.precursorintelligence.com/product/juniper/nfx350) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified - [Qfx5100](https://www.precursorintelligence.com/product/juniper/qfx5100) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified - [Qfx5110](https://www.precursorintelligence.com/product/juniper/qfx5110) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified - [Qfx5120](https://www.precursorintelligence.com/product/juniper/qfx5120) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified - [Qfx5130](https://www.precursorintelligence.com/product/juniper/qfx5130) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified - [Qfx5200](https://www.precursorintelligence.com/product/juniper/qfx5200) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified - [Qfx5210](https://www.precursorintelligence.com/product/juniper/qfx5210) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified - [Qfx5220](https://www.precursorintelligence.com/product/juniper/qfx5220) by [Juniper](https://www.precursorintelligence.com/vendors/juniper) (Hardware): version not specified ## How do I fix CVE-2021-0207? 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/JSA11097) (Vendor advisory) ## Questions ### What is CVE-2021-0207? 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. ### How serious is CVE-2021-0207? 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. ### Is CVE-2021-0207 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 1.3%. That can change at any time, which is why we keep watching. ### Which versions does CVE-2021-0207 affect? 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. ### How do I fix CVE-2021-0207? 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-2021-0207 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. Start free (no card, nothing to install): https://www.precursorintelligence.com/register Book a demo: https://www.precursorintelligence.com/contact