sys_term.c in telnetd in FreeBSD 7.0-RELEASE and other 7.x versions deletes dangerous environment variables with a method that was valid only in older FreeBSD distributions, which might allow remote attackers to execute arbitrary code by passing a crafted environment variable from a telnet client, as demonstrated by an LD_PRELOAD value that references a malicious library.
CWE-16, CWE-264