CVE-2001-0288: Cisco IOS

High severity, CVSS 7.5. EPSS: 5.4% chance of exploitation in the next 30 days.

Cisco switches and routers running IOS 12.1 and earlier produce predictable TCP Initial Sequence Numbers (ISNs), which allows remote attackers to spoof or hijack TCP connections.

Affected products

• Cisco IOS: up to and including 12.1

Published 2001-05-03. Last modified 2026-06-16.