What is CVE-2021-0289?A medium-severity flaw in Junos, explained.
CVE-2021-0289 is a medium-severity flaw (CVSS 5.3) in Junos from Juniper, published on 15 July 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 0.3%. If you run an affected version, plan in the vendor’s fix.
Published 15 July 2021. Record last updated 28 July 2021. We keep this page's data up to date.
What is CVE-2021-0289? In plain terms.
An attacker has to be on the same local network without logging in, and nobody has to click anything. If it works, the attacker can take it offline.
When user-defined ARP Policer is configured and applied on one or more Aggregated Ethernet (AE) interface units, a Time-of-check Time-of-use (TOCTOU) Race Condition vulnerability between the Device Control Daemon (DCD) and firewall process (dfwd) daemons of Juniper Networks Junos OS allows an attacker to bypass the user-defined ARP Policer. In this particular case the User ARP policer is replaced with default ARP policer. To review the desired ARP Policers and actual state one can run the command "show interfaces extensive" and review the output. See further details below. An example output is: show interfaces extensive | match policer Policer: Input: __default_arp_policer__ <<< incorrect if user ARP Policer was applied on an AE interface and the default ARP Policer is displayed Policer: Input: jtac-arp-ae5.317-inet-arp <<< correct if user ARP Policer was applied on an AE interface For all platforms, except SRX Series: This issue affects Juniper Networks Junos OS: All versions 5.6R1 and all later versions prior to 18.4 versions prior to 18.4R2-S9, 18.4R3-S9 with the exception of 15.1 versions 15.1R7-S10 and later versions; 19.4 versions prior to 19.4R3-S3; 20.1 versions prior to 20.1R3; 20.2 versions prior to 20.2R3-S2; 20.3 version 20.3R1 and later versions; 20.4 versions prior to 20.4R3; 21.1 versions prior to 21.1R2; This issue does not affect Juniper Networks Junos OS versions prior to 5.6R1. On SRX Series this issue affects Juniper Networks Junos OS: 18.4 versions prior to 18.4R2-S9, 18.4R3-S9; 19.4 versions prior to 19.4R3-S4; 20.1 versions prior to 20.1R3; 20.2 versions prior to 20.2R3-S2; 20.3 version 20.3R1 and later versions; 20.4 versions prior to 20.4R3; 21.1 versions prior to 21.1R2. This issue does not affect 18.4 versions prior to 18.4R1 on SRX Series. This issue does not affect Junos OS Evolved.
What kind of flaw is it?
- CWE-367Time-of-check Time-of-use (TOCTOU) Race Condition
How an attack on it works
Read straight from its severity rating, translated out of the shorthand.
- Where an attacker can beOn the same local network
- How hard it is to pull offHard: conditions must line up
- 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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Is CVE-2021-0289 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 0.3%. That can change at any time, which is why we keep watching.
Timeline
- Published
- Record last updated
CVE-2021-0289 scores 21. Action: Monitor.
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-2021-0289 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-2021-0289? 229 products.
The published record lists 229 products from 1 vendor. Versions are shown as published: "5.7 to before 15.1" means from 5.7 up to, but not including, 15.1. If you run one of these, check your version, then go to the fix below.
- Operating system
Junos
by Juniper
Affected versions5.6-r15.7 to before 15.115.2 to before 18.418.418.4-r118.4-r1-s118.4-r1-s218.4-r1-s318.4-r1-s418.4-r1-s518.4-r1-s618.4-r1-s718.4-r218.4-r2-s1 - Hardware
Netscreen-Idp
by Juniper
Affected versions3.03.0r13.0r2 - Hardware
Jatp
by Juniper
Affected versions400700 - Hardware
Acx1000
by Juniper
Affected versionsversion not specified - Hardware
Acx1100
by Juniper
Affected versionsversion not specified - Hardware
Acx2000
by Juniper
Affected versionsversion not specified - Hardware
Acx2100
by Juniper
Affected versionsversion not specified - Hardware
Acx2200
by Juniper
Affected versionsversion not specified - Hardware
Acx4000
by Juniper
Affected versionsversion not specified
How do I fix CVE-2021-0289? 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-2021-0289 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
When user-defined ARP Policer is configured and applied on one or more Aggregated Ethernet (AE) interface units, a Time-of-check Time-of-use (TOCTOU) Race Co...
- 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-2021-0289 is a medium-severity flaw in Junos from Juniper, published on 15 July 2021. An attacker has to be on the same local network without logging in, and nobody has to click anything. If it works, the attacker can take it offline.
It scores 5.3 out of 10 on the CVSS severity scale, which is medium. Our risk score for CVE-2021-0289 is 21 out of 100, which is Low. Its action is "Monitor". 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 0.3%. That can change at any time, which is why we keep watching.
For Junos from Juniper: 5.6-r1, 5.7 to before 15.1, 15.2 to before 18.4, 18.4, 18.4-r1, 18.4-r1-s1 and 62 more. The record lists 229 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.