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Securitate DNS |
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 O noua problema de securitate legata de DNS va apare in curand
Dan Kaminsky, unul din expertii in securitate recunoscuti pe plan international, a anuntat ca in curand a lucrat impreuna cu Microsoft, Cisco, Sun, pentru realizarea unui patch de securitate pentru serverele de DNS care va fi instalat simultan. Problema de securitate nu a fost dezvaluita publica in detaliu, ceea ce inseamna ca impactul este major. Teoretic, orice utilizator, chiar daca va scrie in browser adresa unui site corect, poate fi redirectat catre un site fals, deoarece serverele DNS vulnerabile accepta in cache intrari fara verificarea sursei.
In urmatoarea luna, Kaminsky nu va face publice detaliile tehnice, pentru a lasa companiile sa isi faca update.
Multiple Cisco products are vulnerable to DNS cache poisoning attacks due
to their use of insufficiently randomized DNS transaction IDs and UDP
source ports in the DNS queries that they produce, which may allow an
attacker to more easily forge DNS answers that can poison DNS caches.
To exploit this vulnerability an attacker must be able to cause a
vulnerable DNS server to perform recursive DNS queries. Therefore, DNS
servers that are only authoritative, or servers where recursion is not
allowed, are not affected.
Cisco has released free software updates that address these
vulnerabilities.
DETAILS
Vulnerable Products:
The following Cisco products are capable of acting as DNS servers and have
been found to have the DNS implementation weakness that makes some types
of DNS cache poisoning attacks more likely to succeed:
* Cisco IOS Software
A device that is running Cisco IOS Software will be affected if it is
running a vulnerable version and if it is acting as a DNS server.
All Cisco IOS Software releases that support the DNS server functionality
and that have not had their DNS implementation improved are affected. For
information about specific fixed versions, please refer to the Software
Versions and Fixes section.
A device that is running Cisco IOS Software is configured to act as a DNS
server if the command ip dns server is present in the configuration. This
command is not enabled by default.
* Cisco Network Registrar
All Cisco Network Registrar versions are affected, and DNS services are
enabled by default.
The DNS server on CNR is enabled via the command-line interface (CLI)
commands server dns enable start-on-reboot or dns enable start-on-reboot
or via the web management interface in the Servers page by selecting the
appropriate "Start," "Stop," or "Reload" button.
* Cisco Application and Content Networking System
All Cisco Application and Content Networking System (ACNS) versions are
affected; DNS services are disabled by default.
ACNS is configured to act as a DNS server if the command dns enable is
present in the configuration.
* Cisco Global Site Selector Used in Combination with Cisco Network
Registrar
The Cisco Global Site Selector (GSS) is affected when it is used in
combination with Cisco Network Registrar software to provide a more
complete DNS solution. Fixed software would come in the form of an update
of the Cisco Network Registrar software rather than an update of the GSS
software.
Products Confirmed Not Vulnerable:
Products that do not offer DNS server capabilities are not affected by
this vulnerability.
The Cisco GSS by itself is not affected by this vulnerability. However, it
is affected when it is used with Cisco Network Registrar software.
No other Cisco products are currently known to be affected by these
vulnerabilities.
Details:
The Domain Name System is an integral part of networks that are based on
TCP/IP such as the Internet. Simply stated, the Domain Name System is a
hierarchical database that contains mappings of hostnames and IP
addresses. The DNS protocol is part of the TCP/IP protocol suite and
allows DNS clients to query the DNS database to resolve hostnames to IP
addresses.
A DNS server is an application that implements the DNS protocol and that
has the ability to respond to queries made by DNS clients. When handling a
query from a DNS client, a DNS server can look into its portion of the
global DNS database (if the query is for a portion of the DNS database for
which the DNS server is authoritative), or it can relay the query to other
DNS servers (if it is configured to do so and if the query is for a
portion of the DNS database for which the DNS server is not
authoritative.)
Because of the processing time and bandwidth that is associated with
handling a DNS query, most DNS servers locally store responses that are
received from other DNS servers. The area where these responses are stored
locally is called a "cache." Once a response is stored in a cache, the DNS
server can use the locally stored response for a certain time (called the
"time to live") before having to query DNS servers again to refresh the
local (cached) copy of the response.
A DNS cache poisoning attack is an attack in which an entry in the DNS
cache of a DNS server is changed so the IP address associated with a
hostname in the cache does not point to the correct place. For example, if
www.example.com is mapped to the IP address 192.168.0.1 and this mapping
is present in the cache of a DNS server, an attacker who succeeds in
poisoning the DNS cache of this server may be able to map www.example.com
to 10.0.0.1 instead. If this happens, a user who is trying to visit
www.example.com may end up contacting the wrong web server.
Although DNS cache poisoning attacks are not new, a security researcher
recently presented a technique that allows an attacker to mount successful
DNS cache poisoning attacks with low complexity tools and low traffic
requirements. This technique exploits a weakness in most implementations
of the DNS protocol. The fundamental implementation weakness is that the
DNS transaction ID and source port number used to validate DNS responses
are not sufficiently randomized and can easily be predicted, which allows
an attacker to create forged responses to DNS queries that will match the
expected values. The DNS server will consider such responses to be valid.
The following Cisco products that offer DNS server functionality have been
found to be susceptible to DNS cache poisoning attacks:
* Cisco IOS Software: The vulnerability documented in Cisco bug ID
<http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCso81854> CSCso81854 ( registered customers only) .
* Cisco Network Registrar: The vulnerability documented in Cisco bug ID
<http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCsq01298> CSCsq01298 ( registered customers only) .
* Cisco Application and Content Networking System (ACNS): The
vulnerability documented in Cisco bug ID
<http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCsq21930> CSCsq21930 ( registered customers only) .
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-1447>
CVE-2008-1447
Impact:
Successful exploitation of the vulnerability described in this document
may result in invalid hostname-to-IP address mappings in the cache of an
affected DNS server. This may lead users of this DNS server to contact the
wrong provider of network services. The ultimate impact varies greatly,
ranging from a simple denial of service (for example, making
www.example.com resolve to 127.0.0.1) to phishing and financial fraud. |
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