The fetch_url function in usr.bin/ftp/fetch.c in tnftp, as used in NetBSD 5.1 through 5.1.4, 5.2 through 5.2.2, 6.0 through 6.0.6, and 6.1 through 6.1.5 allows remote attackers to execute arbitrary commands via a | (pipe) character at the end of an HTTP redirect.