# What is CVE-2021-1439? > CVE-2021-1439 is a high-severity flaw (CVSS 7.4) in Aironet Access Point Software from Cisco, published on 24 March 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 0.4%. If you run an affected version, plan in the vendor’s fix. Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-1439 ## 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 7.4 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:** 0.4% (latest exploit-likelihood forecast) - **Published:** 24 March 2021 - **Record last updated:** 7 November 2023 - **Main product:** Aironet Access Point Software from Cisco - **Affected products:** 13 ## What is CVE-2021-1439? 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. ### The official description A vulnerability in the multicast DNS (mDNS) gateway feature of Cisco Aironet Series Access Points Software could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient input validation of incoming mDNS traffic. An attacker could exploit this vulnerability by sending a crafted mDNS packet to an affected device through a wireless network that is configured in FlexConnect local switching mode or through a wired network on a configured mDNS VLAN. A successful exploit could allow the attacker to cause the access point (AP) to reboot, resulting in a DoS condition. ### What kind of flaw is it? - CWE-120: Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') ### How an attack on it works - Where an attacker can be: On the same local network - 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:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H` ## Is CVE-2021-1439 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 0.4%. That can change at any time, which is why we keep watching. Exploit likelihood over the last 7 days: 0.4%, 0.4%, 0.4%, 0.4%, 0.4%, 0.4%, 0.4%. ### Timeline - 24 March 2021: Published - 7 November 2023: Record last updated ### How Precursor Intelligence ranks it CVE-2021-1439 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-2021-1439? The published record lists 13 products. Versions are as published: "17.1 to before 17.3.3" means from 17.1 up to, but not including, 17.3.3. - [Aironet Access Point Software](https://www.precursorintelligence.com/product/cisco/aironet_access_point_software) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Application): version not specified - [1100 Integrated Services Router](https://www.precursorintelligence.com/product/cisco/1100_integrated_services_router) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified - [Aironet 1540](https://www.precursorintelligence.com/product/cisco/aironet_1540) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified - [Aironet 1560](https://www.precursorintelligence.com/product/cisco/aironet_1560) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified - [Aironet 1800](https://www.precursorintelligence.com/product/cisco/aironet_1800) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified - [Aironet 2800](https://www.precursorintelligence.com/product/cisco/aironet_2800) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified - [Aironet 3800](https://www.precursorintelligence.com/product/cisco/aironet_3800) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified - [Aironet 4800](https://www.precursorintelligence.com/product/cisco/aironet_4800) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified - [Catalyst 9100](https://www.precursorintelligence.com/product/cisco/catalyst_9100) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified - [Catalyst 9800](https://www.precursorintelligence.com/product/cisco/catalyst_9800) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified - [Catalyst 9800 Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_9800_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 17.1 to before 17.3.3 - [Catalyst Iw6300](https://www.precursorintelligence.com/product/cisco/catalyst_iw6300) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified - [Esw6300](https://www.precursorintelligence.com/product/cisco/esw6300) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified ## How do I fix CVE-2021-1439? 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 - [tools.cisco.com](https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-aironet-mdns-dos-E6KwYuMx) (Vendor advisory) ## Questions ### What is CVE-2021-1439? CVE-2021-1439 is a high-severity flaw in Aironet Access Point Software from Cisco, published on 24 March 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. ### How serious is CVE-2021-1439? It scores 7.4 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2021-1439 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-2021-1439 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 0.4%. That can change at any time, which is why we keep watching. ### Which versions does CVE-2021-1439 affect? For Aironet Access Point Software from Cisco: version not specified. The record lists 13 products in all, each with its versions, under "Who is affected" on this page. ### How do I fix CVE-2021-1439? 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-2021-1439 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