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Vigil@nce: BIND, infinite loop via RRSIG

July 2010 by Vigil@nce

This bulletin was written by Vigil@nce : http://vigilance.fr/

SYNTHESIS OF THE VULNERABILITY

An attacker can send a query for a RRSIG, in order to force BIND
to indefinitely sends queries to authoritative DNS servers.

 Severity: 2/4
 Creation date: 16/07/2010

DESCRIPTION OF THE VULNERABILITY

The DNS protocol defines the RRSIG type which contains the
signature of Resource Records located in the Answer and Authority
sections. There are as many RRSIG as signed name,type,class
triplets in the DNS answer.

In the normal case, when a DNS query asks a RR, the answer
contains this RR and its RRSIG. However, an attacker can directly
ask the RRSIG, which generates an infinite loop in the following
case:
 the attacker queries a recursive DNS server, and
 the DNS server has Trust Anchors (DLV - DNSSEC Lookaside
Validation), and
 the RRSIG is not already in the DNS server cache.
In this case, the DNS server indefinitely sends queries to
authoritative DNS servers for the RRSIG zone.

An attacker can therefore send a query for a RRSIG, in order to
force BIND to indefinitely sends queries to authoritative DNS
servers.

ACCESS TO THE COMPLETE VIGIL@NCE BULLETIN

http://vigilance.fr/vulnerability/BIND-infinite-loop-via-RRSIG-9769


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