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BIND: Weak random number generation


1.  Gentoo Linux Security Advisory

Version Information

Advisory Reference GLSA 200708-13 / bind
Release Date August 18, 2007
Latest Revision August 18, 2007: 01
Impact normal
Exploitable remote
Package Vulnerable versions Unaffected versions Architecture(s)
net-dns/bind < 9.4.1_p1 >= 9.4.1_p1 All supported architectures

Related bugreports: #186556


The ISC BIND random number generator uses a weak algorithm, making it easier to guess the next query ID and perform a DNS cache poisoning attack.

2.  Impact Information


ISC BIND is the Internet Systems Consortium implementation of the Domain Name System (DNS) protocol.


Amit Klein from Trusteer reported that the random number generator of ISC BIND leads, half the time, to predictable (1 chance to 8) query IDs in the resolver routine or in zone transfer queries (CVE-2007-2926). Additionally, the default configuration file has been strengthen with respect to the allow-recursion{} and the allow-query{} options (CVE-2007-2925).


A remote attacker can use this weakness by sending queries for a domain he handles to a resolver (directly to a recursive server, or through another process like an email processing) and then observing the resulting IDs of the iterative queries. The attacker will half the time be able to guess the next query ID, then perform cache poisoning by answering with those guessed IDs, while spoofing the UDP source address of the reply. Furthermore, with empty allow-recursion{} and allow-query{} options, the default configuration allowed anybody to make recursive queries and query the cache.

3.  Resolution Information


There is no known workaround at this time for the random generator weakness. The allow-recursion{} and allow-query{} options should be set to trusted hosts only in /etc/bind/named.conf, thus preventing several security risks.


All ISC BIND users should upgrade to the latest version:

Code Listing 3.1: Resolution

# emerge --sync
# emerge --ask --oneshot --verbose ">=net-dns/bind-9.4.1_p1"

4.  References


Page updated August 18, 2007

Summary: This is a Gentoo Linux Security Advisory

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