diff -ur tcpdump-2004.01.21/tcpdump.1 tcpdump-2004.01.21.droproot/tcpdump.1
--- tcpdump-2004.01.21/tcpdump.1	Thu Jan 15 21:55:56 2004
+++ tcpdump-2004.01.21.droproot/tcpdump.1	Wed Jan 21 19:36:41 2004
@@ -83,6 +83,10 @@
 .B \-y
 .I datalinktype
 ]
+[
+.B \-Z
+.I user
+]
 .ti +8
 [
 .I expression
@@ -541,6 +545,12 @@
 .TP
 .B \-y
 Set the data link type to use while capturing packets to \fIdatalinktype\fP.
+.TP
+.B \-Z
+Drops privileges (if root) and changes user ID to
+.I user
+and the group ID to the primary group of
+.IR user .
 .IP "\fI expression\fP"
 .RS
 selects which packets will be dumped.
Only in tcpdump-2004.01.21.droproot: tcpdump.1.orig
diff -ur tcpdump-2004.01.21/tcpdump.c tcpdump-2004.01.21.droproot/tcpdump.c
--- tcpdump-2004.01.21/tcpdump.c	Thu Jan 15 21:56:50 2004
+++ tcpdump-2004.01.21.droproot/tcpdump.c	Wed Jan 21 19:33:42 2004
@@ -65,6 +65,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <pwd.h>
 
 #include "interface.h"
 #include "addrtoname.h"
@@ -310,6 +311,25 @@
 #define U_FLAG
 #endif
 
+/* Drop root privileges */
+void droproot(const char *username)
+{
+	struct passwd *pw = NULL;
+	pw = getpwnam(username);
+	if (pw) {
+		if (initgroups(pw->pw_name, NULL) != 0 || setgid(pw->pw_gid) != 0 ||
+				 setuid(pw->pw_uid) != 0) {
+			fprintf(stderr, "Couldn't change to '%.32s' uid=%d gid=%d\n", username, 
+							pw->pw_uid, pw->pw_gid);
+			exit(1);
+		}
+	}
+	else {
+		fprintf(stderr, "Couldn't find user '%.32s'\n", username);
+		exit(1);
+	}
+}
+
 int
 main(int argc, char **argv)
 {
@@ -326,6 +346,7 @@
 	struct dump_info dumpinfo;
 	u_char *pcap_userdata;
 	char ebuf[PCAP_ERRBUF_SIZE];
+	char *username = NULL;
 #ifdef HAVE_PCAP_FINDALLDEVS
 	pcap_if_t *devpointer;
 	int devnum;
@@ -355,7 +376,7 @@
 
 	opterr = 0;
 	while (
-	    (op = getopt(argc, argv, "aA" B_FLAG "c:C:d" D_FLAG "eE:fF:i:lLm:nNOpqr:Rs:StT:u" U_FLAG "vw:xXy:Y")) != -1)
+	    (op = getopt(argc, argv, "aA" B_FLAG "c:C:d" D_FLAG "eE:fF:i:lLm:nNOpqr:Rs:StT:u" U_FLAG "vw:xXy:YZ:")) != -1)
 		switch (op) {
 
 		case 'a':
@@ -619,6 +640,16 @@
 			}
 			break;
 #endif
+		case 'Z':
+			if (optarg) {
+				username = strdup(optarg);
+			}
+			else {
+				usage();
+				/* NOTREACHED */
+			}
+			break;
+
 		default:
 			usage();
 			/* NOTREACHED */
@@ -641,7 +672,13 @@
 		 * people's trace files (especially if we're set-UID
 		 * root).
 		 */
-		setuid(getuid());
+		if (username) {
+			droproot(username);
+		}
+		else {
+			if (setgid(getgid()) != 0 || setuid(getuid()) != 0 )
+				fprintf(stderr, "Warning: setgid/setuid failed !\n");
+		}
 #endif /* WIN32 */
 		pd = pcap_open_offline(RFileName, ebuf);
 		if (pd == NULL)
@@ -729,7 +766,13 @@
 		 * Let user own process after socket has been opened.
 		 */
 #ifndef WIN32
-		setuid(getuid());
+		if (username) {
+			droproot(username);
+		}
+		else {
+			if (setgid(getgid()) != 0 || setuid(getuid()) != 0)
+				fprintf(stderr, "Warning: setgid/setuid failed !\n");
+		}
 #endif /* WIN32 */
 	}
 	if (infile)
@@ -1167,7 +1210,7 @@
 	(void)fprintf(stderr,
 "\t\t[ -E algo:secret ] [ -F file ] [ -i interface ] [ -r file ]\n");
 	(void)fprintf(stderr,
-"\t\t[ -s snaplen ] [ -T type ] [ -w file ] [ -y datalinktype ]\n");
+"\t\t[ -s snaplen ] [ -T type ] [ -w file ] [ -y datalinktype ] [ -Z user ]\n");
 	(void)fprintf(stderr,
 "\t\t[ expression ]\n");
 	exit(1);
Only in tcpdump-2004.01.21.droproot: tcpdump.c.orig