CVE-2021-1439

Cisco Aironet Access Points FlexConnect Multicast DNS Denial of Service Vulnerability

HIGH

7.4

CVSS Score

Published: March 24, 2021 at 08:05 PM UTC

Updated: June 17, 2026 at 03:31 AM UTC

13 products affected across 1 vendorAironet Access PointCatalyst 9800 Firmware1100 Integrated Services Router

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Severity

HIGH7.4

Exploit prediction

EPSS 0.4%

SSVC

No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Aironet Access Point · Cisco

95%

All versions

cisco-1100-integrated-services-router (environment) · cisco-aironet-1540 (environment) · cisco-aironet-1560 (environment) · cisco-aironet-1800 (environment) · cisco-aironet-2800 (environment) · cisco-aironet-3800 (environment) · cisco-aironet-4800 (environment) · cisco-catalyst-9100 (environment) · cisco-catalyst-iw6300 (environment) · cisco-esw6300 (environment)

Catalyst 9800 Firmware · Cisco

95%

17.1 ≤ v < 17.3.3

Affected range stops below 17.3.3, so it looks safe — our inference, not a vendor statement

cisco-catalyst-9800 (same device)

1100 Integrated Services Router · Ciscodevice

80%

All versions

Aironet 1540 · Ciscodevice

80%

All versions

Aironet 1560 · Ciscodevice