It's possible to lock user's account if user's password is stored as NT-hash via HTTP proxy. Service restart or configuration reload is required to restore account in working state. In addition, Basic authentication is offered as first authentication protocol, it can lead to shoosing weak (cleartext) authentication protocol even if stronger one (NTLM) supported. Vulnerability is fixed in 0.5.3 version.
CVE-2006-6982 (3proxy 0.5 to 0.5.2 does not offer NTLM authentication before basic authentication, which might cause browsers with incomplete RFC2616/RFC2617 support to use basic cleartext authentication even if NTLM is available, which makes it easier for attackers to steal credentials.)
CVE-2006-6981 (3proxy 0.5 to 0.5.2, when NT-encoded passwords are being used, allows remote attackers to cause a denial of service (blocked account) via unspecified vectors related to NTLM authentication, which causes a password hash to be overwritten.)