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CWE-350: Reliance on Reverse DNS Resolution for a Security-Critical Action

Weakness ID: 350
Abstraction: Variant
Structure: Simple
Status: Draft
Presentation Filter:
+ Description
The software performs reverse DNS resolution on an IP address to obtain the hostname and make a security decision, but it does not properly ensure that the IP address is truly associated with the hostname.
+ Extended Description

Since DNS names can be easily spoofed or misreported, and it may be difficult for the software to detect if a trusted DNS server has been compromised, DNS names do not constitute a valid authentication mechanism.

When the software performs a reverse DNS resolution for an IP address, if an attacker controls the server for that IP address, then the attacker can cause the server to return an arbitrary hostname. As a result, the attacker may be able to bypass authentication, cause the wrong hostname to be recorded in log files to hide activities, or perform other attacks.

Attackers can spoof DNS names by either (1) compromising a DNS server and modifying its records (sometimes called DNS cache poisoning), or (2) having legitimate control over a DNS server associated with their IP address.

+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Development Concepts" (CWE-699)
ChildOfBaseBase290Authentication Bypass by Spoofing
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Architecture and Design
+ Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.


Class: Language-Independent (Undetermined Prevalence)

+ Common Consequences

The table below specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

Access Control

Technical Impact: Gain Privileges or Assume Identity; Bypass Protection Mechanism

Malicious users can fake authentication information by providing false DNS information.
+ 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.

(bad code)
Example Language:
struct hostent *hp;struct in_addr myaddr;
char* tHost = "";

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("")) {
trusted = true;

(bad code)
Example Language: C# 
IPAddress hostIPAddress = IPAddress.Parse(RemoteIpAddress);
IPHostEntry hostInfo = Dns.GetHostByAddress(hostIPAddress);
if (hostInfo.HostName.EndsWith("")) {
trusted = true;


If an attacker can poison the DNS cache, they can gain trusted status.

Example 2

In these examples, a connection is established if a request is made by a trusted host.

(bad code)
Example Language:
sd = socket(AF_INET, SOCK_DGRAM, 0);
serv.sin_family = AF_INET;
serv.sin_addr.s_addr = htonl(INADDR_ANY);
servr.sin_port = htons(1008);
bind(sd, (struct sockaddr *) & serv, sizeof(serv));
while (1) {

memset(msg, 0x0, MAX_MSG);
clilen = sizeof(cli);
if (h->h_name==...) n = recvfrom(sd, msg, MAX_MSG, 0, (struct sockaddr *) & cli, &clilen);

(bad code)
Example Language: Java 
while(true) {
DatagramPacket rp=new DatagramPacket(rData,rData.length);
String in = new String(p.getData(),0, rp.getLength());
InetAddress IPAddress = rp.getAddress();
int port = rp.getPort();
if ((rp.getHostName()==...) & (in==...)) {

out = secret.getBytes();
DatagramPacket sp =new DatagramPacket(out,out.length, IPAddress, port);



These examples check if a request is from a trusted host before responding to a request, but the code only verifies the hostname as stored in the request packet. An attacker can spoof the hostname, thus impersonating a trusted client.

+ Observed Examples
Does not do double-reverse lookup to prevent DNS spoofing.
Does not verify reverse-resolved hostnames in DNS.
Authentication bypass using spoofed reverse-resolved DNS hostnames.
Authentication bypass using spoofed reverse-resolved DNS hostnames.
Filter does not properly check the result of a reverse DNS lookup, which could allow remote attackers to bypass intended access restrictions via DNS spoofing.
Reverse DNS lookup used to spoof trusted content in intermediary.
Product records the reverse DNS name of a visitor in the logs, allowing spoofing and resultant XSS.
+ Potential Mitigations

Phase: Architecture and Design

Use other means of identity verification that cannot be simply spoofed. Possibilities include a username/password or certificate.

Phase: Implementation

Perform proper forward and reverse DNS lookups to detect DNS spoofing.
+ Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
+ Notes


CWE-350, CWE-247, and CWE-292 were merged into CWE-350 in CWE 2.5. CWE-247 was originally derived from Seven Pernicious Kingdoms, CWE-350 from PLOVER, and CWE-292 from CLASP. All taxonomies focused closely on the use of reverse DNS for authentication of incoming requests.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERImproperly Trusted Reverse DNS
CLASPTrusting self-reported DNS name
Software Fault PatternsSFP29Faulty endpoint authentication
+ References
[REF-44] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 15: Not Updating Easily." Page 231. McGraw-Hill. 2010.
[REF-44] 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-62] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 16, "DNS Spoofing", Page 1002. 1st Edition. Addison Wesley. 2006.
+ Content History
Submission DateSubmitterOrganization
Modification DateModifierOrganization
2008-07-01Sean EidemillerCigital
added/updated demonstrative examples
2008-09-08CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2009-05-27CWE Content TeamMITRE
updated Relationships
2010-09-27CWE Content TeamMITRE
updated Potential_Mitigations
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2012-05-11CWE Content TeamMITRE
updated Related_Attack_Patterns, Relationships
2013-06-23CWE Content TeamMITRE
CWE-247 and CWE-292 deprecated and merged into CWE-350 to address duplicates.
2013-07-17CWE Content TeamMITRE
updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Description, Maintenance_Notes, Name, Potential_Mitigations, References, Relationships, Taxonomy_Mappings, Type
2014-02-18CWE Content TeamMITRE
updated Description, Relationships
2014-07-30CWE Content TeamMITRE
updated Demonstrative_Examples, Relationships, Taxonomy_Mappings
2017-05-03CWE Content TeamMITRE
updated Related_Attack_Patterns
2017-11-08CWE Content TeamMITRE
updated Demonstrative_Examples, Relationships
Previous Entry Names
Change DatePrevious Entry Name
2013-07-17Improperly Trusted Reverse DNS

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Page Last Updated: January 18, 2018