What is CVE-2020-3118?A high-severity flaw criminals are using now.
CVE-2020-3118 is a high-severity flaw (CVSS 8.8) in IOS XR from Cisco, published on 5 February 2020. It is on the list of flaws known to be exploited, so criminals are already using it. The latest forecast puts its chance of use in the next 30 days at 12%. If you run an affected version, patch it first.
Published 5 February 2020. Record last updated 28 October 2025. We keep this page's data up to date.
What is CVE-2020-3118? 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 read data, change data and take it offline.
A vulnerability in the Cisco Discovery Protocol implementation for Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to execute arbitrary code or cause a reload on an affected device. The vulnerability is due to improper validation of string input from certain fields in Cisco Discovery Protocol messages. An attacker could exploit this vulnerability by sending a malicious Cisco Discovery Protocol packet to an affected device. A successful exploit could allow the attacker to cause a stack overflow, which could allow the attacker to execute arbitrary code with administrative privileges on an affected device. Cisco Discovery Protocol is a Layer 2 protocol. To exploit this vulnerability, an attacker must be in the same broadcast domain as the affected device (Layer 2 adjacent).
What kind of flaw is it?
- CWE-787Out-of-bounds Write
- CWE-134Use of Externally-Controlled Format String
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 offEasy: no special conditions
- Login needed firstNo login needed
- Does someone have to clickNo, nobody has to do anything
- What an attacker getsCan read data, change data and take it offline
Severity vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Is CVE-2020-3118 being exploited? Yes.
Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at 12%.
Timeline
- Published
- Record last updated
- Exploit likelihood jumped
CVE-2020-3118 scores 74. Action: Emergency patch.
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-2020-3118 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-2020-3118? One product.
The published record lists 1 product from 1 vendor. Versions are shown as published: "6.6.0 to before 6.6.12" means from 6.6.0 up to, but not including, 6.6.12. If you run one of these, check your version, then go to the fix below.
How do I fix CVE-2020-3118? 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.
- Check it wasn’t used before you patchedBecause criminals are already using this flaw, look for signs of a break-in on affected systems using the vendor’s guidance.
Does CVE-2020-3118 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.
Free plan, no card needed. Nothing to install.
1 flaw being exploited affects software Acme tracks
A vulnerability in the Cisco Discovery Protocol implementation for Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to execute arbitra...
- Matched to
- IOS XR on Acme's software list
- What to do
- Patch first, then check for signs of use
Sent to the alert recipients Acme chose. Also in the app and to Acme's webhook.
CVE-2020-3118 is a high-severity flaw in IOS XR from Cisco, published on 5 February 2020. 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 read data, change data and take it offline.
It scores 8.8 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2020-3118 is 74 out of 100, which is High. Its action is "Emergency patch". Attackers are using this flaw today. If you run an affected version, it goes to the top of your list.
Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at 12%.
For IOS XR from Cisco: 5.2.5, 6.4.2, 6.5.3, 6.6.0 to before 6.6.12, 6.6.25, 7.0.0 to before 7.0.2.
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. Because criminals are already using it, also check affected systems for signs of a break-in.