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DNS: cache poisoning
Synthesis of the vulnerability
An attacker can predict DNS queries in order to poison the DNS client or cache (caching resolver).
Impacted systems: ProxyRA, ProxySG par Blue Coat, IOS by Cisco, Cisco Router, Debian, Dnsmasq, BIG-IP Hardware, TMOS, Fedora, FreeBSD, MPE/iX, Tru64 UNIX, HP-UX, AIX, BIND, Juniper E-Series, Juniper J-Series, JUNOSe, Junos OS, Mandriva Linux, Mandriva NF, Windows 2000, Windows 2003, Windows 2008 R0, Windows (platform) ~ not comprehensive, Windows XP, NetBSD, NetScreen Firewall, ScreenOS, NLD, Netware, OES, OpenBSD, OpenSolaris, openSUSE, Solaris, Trusted Solaris, DNS protocol, RHEL, Slackware, SLES, TurboLinux, Unix (platform) ~ not comprehensive, ESX.
Severity of this alert: 3/4.
Consequences of an intrusion: data creation/edition.
Pirate's origin: internet server.
Creation date: 09/07/2008.
Revisions dates: 22/07/2008, 24/07/2008, 25/07/2008.
Références of this alert: 107064, 239392, 240048, 6702096, 7000912, 953230, BID-30131, c01506861, c01660723, CAU-EX-2008-0002, CAU-EX-2008-0003, CERTA-2002-AVI-189, CERTA-2002-AVI-200, cisco-sa-20080708-dns, CR102424, CR99135, CSCso81854, CVE-2008-1447, draft-ietf-dnsext-forgery-resilience-05, DSA-1544-2, DSA-1603-1, DSA-1604-1, DSA-1605-1, DSA-1617-1, DSA-1619-1, DSA-1619-2, DSA-1623-1, FEDORA-2008-6256, FEDORA-2008-6281, FEDORA-2009-1069, FreeBSD-SA-08:06.bind, HPSBMP02404, HPSBTU02358, HPSBUX02351, MDVSA-2008:139, MS08-037, NetBSD-SA2008-009, powerdns-advisory-2008-01, PSN-2008-06-040, RHSA-2008:0533-01, RHSA-2008:0789-01, SOL8938, SSA:2008-191-02, SSA:2008-205-01, SSRT080058, SSRT090014, SUSE-SA:2008:033, TA08-190B, TLSA-2008-26, VIGILANCE-VUL-7937, VMSA-2008-0014, VMSA-2008-0014.1, VMSA-2008-0014.2, VU#800113.
Description of the vulnerability
The DNS protocol defines a 16 bit identifier to associate an answer to its query. When attacker predicts this identifier and the UDP port number, he can send fake answers and thus poison the DNS cache.
Most implementation use a fixed port number, which increases the probability of a poisoning success. As there is only one chance of success during the TTL period, and as the poisoning does not work for each trial, this direct and old attack is not practical.
However, instead of poisoning the answer record, the attacker can poison additional records. Indeed, when the DNS client asks the address of www.example.com, the DNS server returns:
www.example.com A 220.127.116.11 (answer)
example.com NS dns.example.com (authoritative)
dns.example.com A 18.104.22.168 (additional)
An attacker can therefore force the client to ask the resolution of several names (via a web page containing images for example): aaa.example.com, aab.example.com, ..., aaz.example.com. In his answers, the attacker then always provides the same additional malicious answer (www.example.com A 22.214.171.124). Even if, for example, only aab.example.com is poisoned, its additional record (www.example.com = 126.96.36.199) will be stored in the cache.
An attacker can therefore poison the DNS cache/client and redirect all users to a malicious site.
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