Cisco VPN 5000 series concentrator hardware 6.0.21.0002 and earlier, and 5.2.23.0003 and earlier, when using RADIUS with a challenge type of Password Authentication Protocol (PAP) or Challenge, sends the user password in cleartext in a validation retry request, which could allow remote attackers to steal passwords via sniffing.
https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2002-0848