Firewall Vulnerabilities Presented by Vincent J. Ohm

Topics Firewall design (Stateful) Packet Filter, Application proxy, Personal Firewall OSI Stack Layer IP, TCP spoofing Applications sendmail Firewall implementation broad permissions, overflows, etc.

Firewalls Network gateway handles incoming & outgoing traffic Access manager blocks/grants access to services, networks

Firewall Design (The benefits) Packet Filter – scans IP address, port number – block specific adresses, ports – Stateful: adds connection filtering Application Proxy – scans packet payload – filter harmful data, program commands Personal – combination of filter & proxy

Firewall Design (The drawbacks) Packet Filter – harmful data passes through Application Proxy – unknown application vulnerabilities

OSI Stack Network – I.P. – no address authentication – address is spoofable Transport – T.C.P. – sequence number enforces exclusivity – spoof I.P. address and guess seq. number... – T.C.P. spoofing

Applications Applications with vulnerabilities –sendmail ‘WIZ’  debugging command creates root shell access on remote server Methods of exploitation –crafted data (overflows) –commands (sendmail) Packet Filters can block some Application Proxies can block more

Firewall Implementation Symantec Firewall/VPN Appliance –Password leak Pyramid BenHur –Active FTP Kerio Personal Firewall –Rules bypassable Cisco PIX –SNMPv3, VPNC IPsec Check Point Firewall-1 & DeleGate application proxy –overflows

Symantec Firewall/VPN Appliance Accessing firewall to change password from unsecured terminal using web browser Firewall’s HTTP response, stored in browser cache HTTP response contains the new password… …in cleartext! Symantec’s fix: strips password data

Pyramid BenHur Firewall Firewall access rules can be bypassed… …by sending connect request with source port = 20  FTP data port Can connect to any port Workaround: block all outside access from port 20 OR apply patch

Kerio Personal Firewall Problem with default configuration Firewall would allow any UDP packet through if source port = 53  DNS port Intention: allow DNS responses Fix: allow packet only if DNS request precedes the response

Check Point Firewall-1 Invalid HTTP request Generates error message using portion of input… …included in format string used for call to sprintf() Exploit for: –command execution on firewall –arbitrary code execution

DeleGate Application Proxy Uses fixed array size for username & password Arrays used in calls to strcpy() Input sufficiently long strings… …buffer overflow!

Conclusion Firewalls are not invulnerable Vulnerable by … –Design –Other O.S.I. Layers vulnerabilities –Implementation flawes flaws