3proxy from 0.9.7 through 1.0.1, fixed in commit 206c923, contains an uninitialized stack memory disclosure vulnerability that allows unauthenticated attackers to leak stack bytes via the SOCKS4 reply path when the external-NAT option (-Ne) is configured. Attackers can send a client probe that fails the SOCKS version check to trigger a reply containing uninitialized bytes from the sin structure, exposing high bytes of a userspace pointer that weakens ASLR protections.

Double free vulnerability in the ftpprchild function in ftppr in 3proxy 0.5 through 0.5.3i allows remote attackers to cause a denial of service (daemon crash) via multiple OPEN commands to the FTP proxy.

Buffer overflow in the HTTP proxy service for 3proxy 0.5 to 0.5.3g, and 0.6b-devel before 20070413, might allow remote attackers to execute arbitrary code via crafted transparent requests.

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.

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.