Date: Tue, 7 Nov 2000 13:40:49 +0100 From: "Fabio Pietrosanti (naif)" <fabio@TELEMAIL.IT> Subject: BIND 8.2.2-P5 Possible DOS To: BUGTRAQ@SECURITYFOCUS.COM Hi, playing with bind and ZXFR feature ( zone transfer compressed with a possible insecure execlp("gzip", "gzip", NULL); ), i discovered a Denial Of Service against Bind 8.2.2-P5 . By default Bind 8.2.2-P5 it's not compiled with ZXFR support unless you define it with #define BIND_ZXFR so it will refuse any ZXFR transfer, because it doesn't support it. But now what appens? Look here... ################################ zone to transfer: zone.pippo.com dns server: dns.pippo.com 192.168.1.1 me: naif.gatesux.com 10.10.10.10 I send a Zone Trasnfer request using "-Z" switch with means that i wish to use ZXFR. dns.pippo.com does'nt support ZXFR and have "allow-transfer{}" not configured, so everyone could ask him for *.zone.pippo.com ... <naif@naif> [~/bind/src822p5/bin/named-xfer] $ ./named-xfer -z zone.pippo.com -d 9 -f pics -Z dns.pippo.com named-xfer[29297]: send AXFR query 0 to 192.168.1.1 named-xfer[29297]: premature EOF, fetching "zone.pippo.com" On the server's log: Nov 7 11:19:09 dns.pippo.com: named[188510]: approved ZXFR from [10.10.10.10].2284 for "zone.pippo.com" Nov 7 11:19:09 dns.pippo.com: named[188510]: unsupported XFR (type ZXFR) of "zone.pippo.com" (IN) to [10.10.10.10].2284 Then the server "*** CRASHED ***" . I should assume that bind 8.2.2-P5 it's vulnerable ( Please someone test and confirm this kind of dos) and bind-9.0.0 has no support for ZXFR . <naif@naif> [~/bind] $ find src822p5/ -type f -exec grep -i zxfr \{\} ';' | wc -l 234 <naif@naif> [~/bind] $ find bind-9.0.0/ -type f -exec grep -i zxfr \{\} ';' | wc -l 0 A lot of DNS Server are misconfigured, and allow zone-transfer to any, so they are dossable... naif naif@itapac.net