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What is CVE-2021-1389?A medium-severity flaw in IOS XR, explained.

Medium severity12 affected products
The short answer

CVE-2021-1389 is a medium-severity flaw (CVSS 6.5) in IOS XR from Cisco, published on 4 February 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 1.2%. If you run an affected version, plan in the vendor’s fix.

Check if it affects you →How to fix it

Published 4 February 2021. Record last updated 7 November 2023. We keep this page's data up to date.

What it does

What is CVE-2021-1389? 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 read some data and change some data.

The official description

A vulnerability in the IPv6 traffic processing of Cisco IOS XR Software and Cisco NX-OS Software for certain Cisco devices could allow an unauthenticated, remote attacker to bypass an IPv6 access control list (ACL) that is configured for an interface of an affected device. The vulnerability is due to improper processing of IPv6 traffic that is sent through an affected device. An attacker could exploit this vulnerability by sending crafted IPv6 packets that traverse the affected device. A successful exploit could allow the attacker to access resources that would typically be protected by the interface ACL.

What kind of flaw is it?

  • CWE-284Improper Access Control
CVSS 3.1 scoreMedium · 6.5

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 read some data and change some data

Severity vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Exploitation

Is CVE-2021-1389 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 1.2%. That can change at any time, which is why we keep watching.

Known to be exploitedNoNot on the list of exploited flaws today
Chance of use in the next 30 days1.2%Its EPSS score, from the latest forecast

Timeline

  1. Published
  2. Record last updated
How Precursor Intelligence ranks it
31out of 100Low

CVE-2021-1389 scores 31. 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-2021-1389 matches software you track, it lands in your list with its score and the reasons behind it.

See your own ranked list →
Affected products

Who is affected by CVE-2021-1389? 12 products.

The published record lists 12 products from 1 vendor. Versions are shown as published: "before 6.6.3" means every version up to, but not including, 6.6.3. If you run one of these, check your version, then go to the fix below.

Remediation

How do I fix CVE-2021-1389? Four steps.

  1. 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.
  2. Apply the vendor’s fixInstall the update named in the vendor’s advisory. We’ve put the advisory first in the list.
  3. 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.
  4. 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 link
Precursor Intelligence

Does CVE-2021-1389 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.

  1. Tell us what you runPick your software from a list, or let us work it out from your website.
  2. We match it to every flawOver 400,000 published flaws, checked against your list.
  3. Ranked by real-world riskA 0 to 100 score, led by evidence criminals are using it.
  4. Told as soon as we knowAn alert by email, in the app or by webhook to your own tools.
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CVE-2021-1389 is a medium-severity flaw in IOS XR from Cisco, published on 4 February 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 read some data and change some data.

It scores 6.5 out of 10 on the CVSS severity scale, which is medium. Our risk score for CVE-2021-1389 is 31 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 1.2%. That can change at any time, which is why we keep watching.

For IOS XR from Cisco: before 6.6.3, 7.1.0, 7.2.0. The record lists 12 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.

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