CVE-2020-3511: Cisco IOS XE

High severity, CVSS 7.4. EPSS: 0.4% chance of exploitation in the next 30 days.

A vulnerability in the ISDN subsystem of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to cause a reload of an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to insufficient input validation when the ISDN Q.931 messages are processed. An attacker could exploit this vulnerability by sending a malicious ISDN Q.931 message to an affected device. A successful exploit could allow the attacker to cause the process to crash, resulting in a reload of the affected device.

Affected products

• Cisco IOS XE: version 15.1(4)m only

Published 2020-09-24. Last modified 2026-06-17.