CWE-247: Reliance on DNS Lookups in a Security Decision
Reliance on DNS Lookups in a Security Decision
Weakness ID: 247 (Weakness Variant)
Status: Incomplete
Description
Description Summary
Attackers can spoof DNS entries. Do not rely on DNS names for security.
Time of Introduction
Implementation
Architecture and Design
Applicable Platforms
Languages
All
Common Consequences
Scope
Effect
Access Control
Technical Impact: Gain privileges / assume
identity; Bypass protection
mechanism
Demonstrative Examples
Example 1
The following code samples use a DNS lookup in order to decide
whether or not an inbound request is from a trusted host. If an attacker can
poison the DNS cache, they can gain trusted status.
(Bad Code)
Example
Language: C
struct hostent *hp;struct in_addr myaddr;
char* tHost = "trustme.example.com";
myaddr.s_addr=inet_addr(ip_addr_string);
hp = gethostbyaddr((char *) &myaddr, sizeof(struct
in_addr), AF_INET);
if (hp && !strncmp(hp->h_name, tHost,
sizeof(tHost))) {
trusted = true;
} else {
trusted = false;
}
(Bad Code)
Example
Language: Java
String ip = request.getRemoteAddr();
InetAddress addr = InetAddress.getByName(ip);
if (addr.getCanonicalHostName().endsWith("trustme.com")) {
IP addresses are more reliable than DNS names, but they can also be
spoofed. Attackers can easily forge the source IP address of the packets
they send, but response packets will return to the forged IP address. To
see the response packets, the attacker has to sniff the traffic between
the victim machine and the forged IP address. In order to accomplish the
required sniffing, attackers typically attempt to locate themselves on
the same subnet as the victim machine. Attackers may be able to
circumvent this requirement by using source routing, but source routing
is disabled across much of the Internet today. In summary, IP address
verification can be a useful part of an authentication scheme, but it
should not be the single factor required for authentication.
Potential Mitigations
Phase: Implementation
Perform proper forward and reverse DNS lookups to detect DNS spoofing.
Other Notes
Many DNS servers are susceptible to spoofing attacks, so you should assume
that your software will someday run in an environment with a compromised DNS
server. If attackers are allowed to make DNS updates (sometimes called DNS
cache poisoning), they can route your network traffic through their machines
or make it appear as if their IP addresses are part of your domain. Do not
base the security of your system on DNS names.
[REF-17] Michael Howard, David LeBlanc
and John Viega. "24 Deadly Sins of Software Security". "Sin 15: Not Updating Easily." Page 231. McGraw-Hill. 2010.
[REF-17] Michael Howard, David LeBlanc
and John Viega. "24 Deadly Sins of Software Security". "Sin 24: Trusting Network Name Resolution." Page
361. McGraw-Hill. 2010.
[REF-7] Mark Dowd, John McDonald
and Justin Schuh. "The Art of Software Security Assessment". Chapter 16, "DNS Spoofing", Page 1002.. 1st Edition. Addison Wesley. 2006.
Description
