What’s Vulnerable › Vulnerabilities

CVE-2020-3511: Cisco IOS and IOS XE Software ISDN Q.931 Denial of Service Vulnerability

• Severity: high (CVSS 7.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-09-24 · updated 2026-06-17
• Weakness: CWE-20

Description

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: 15.1(4)m

References

• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxe-isdn-q931-dos-67eUZBTf
• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxe-isdn-q931-dos-67eUZBTf

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