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Reliance on Reverse DNS Resolution for a Security-Critical Action

Draft Variant
Structure: Simple
Description

This vulnerability occurs when an application uses a reverse DNS lookup on an IP address to get a hostname and then uses that hostname for a security decision—like access control or logging—without verifying that the IP address actually belongs to that hostname.

Extended Description

Relying on a reverse DNS (rDNS) hostname for authentication or security decisions is inherently risky because DNS records are not a secure proof of identity. An attacker who controls the DNS server for their IP address can make it return any hostname they choose, such as 'trusted-server.internal,' potentially bypassing IP allowlists, spoofing logs, or gaining unauthorized access. Attackers can spoof these names either by compromising a legitimate DNS server (via methods like cache poisoning) or by legitimately managing the DNS for their own infrastructure. Since applications cannot easily distinguish between a legitimate rDNS response and a spoofed one, using this data for security-critical actions creates a significant weakness that can be exploited to hide malicious activity or impersonate trusted systems.
Common Consequences 1
Scope: Access Control

Impact: Gain Privileges or Assume IdentityBypass Protection Mechanism

Malicious users can fake authentication information by providing false DNS information.
Detection Methods 1
Automated Static AnalysisHigh
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
Potential Mitigations 2
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.
Demonstrative Examples 2

ID : DX-93

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.

Code Example:

Bad
C
c

Code Example:

Bad
Java
java

Code Example:

Bad
C#
c#
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.
In these examples, a connection is established if a request is made by a trusted host.

Code Example:

Bad
C
c

Code Example:

Bad
Java
java
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 7
CVE-2001-1488Does not do double-reverse lookup to prevent DNS spoofing.
CVE-2001-1500Does not verify reverse-resolved hostnames in DNS.
CVE-2000-1221Authentication bypass using spoofed reverse-resolved DNS hostnames.
CVE-2002-0804Authentication bypass using spoofed reverse-resolved DNS hostnames.
CVE-2001-1155Filter does not properly check the result of a reverse DNS lookup, which could allow remote attackers to bypass intended access restrictions via DNS spoofing.
CVE-2004-0892Reverse DNS lookup used to spoof trusted content in intermediary.
CVE-2003-0981Product records the reverse DNS name of a visitor in the logs, allowing spoofing and resultant XSS.
References 4
The CLASP Application Security Process
Secure Software, Inc.
2005
https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf(2024-11-17)
ID: REF-18
24 Deadly Sins of Software Security
Michael Howard, David LeBlanc, and John Viega
McGraw-Hill
2010
ID: REF-44
24 Deadly Sins of Software Security
Michael Howard, David LeBlanc, and John Viega
McGraw-Hill
2010
ID: REF-44
The Art of Software Security Assessment
Mark Dowd, John McDonald, and Justin Schuh
Addison Wesley
2006
ID: REF-62
Applicable Platforms
Languages:
Not Language-Specific : Undetermined
Modes of Introduction
Architecture and Design
Related Attack Patterns
Related Weaknesses
ChildOf: Authentication Bypass by Spoofing (CWE-290)
ChildOf: Reliance on Untrusted Inputs in a Security Decision (CWE-807)
CanPrecede: Improper Restriction of Communication Channel to Intended Endpoints (CWE-923)
Taxonomy Mapping
  • PLOVER
  • CLASP
  • Software Fault Patterns
Notes
MaintenanceReliance on Reverse DNS Resolution for a Security-Critical Action, DEPRECATED: Reliance on DNS Lookups in a Security Decision, and DEPRECATED: Trusting Self-reported DNS Name were merged into Reliance on Reverse DNS Resolution for a Security-Critical Action in CWE 2.5. DEPRECATED: Reliance on DNS Lookups in a Security Decision was originally derived from Seven Pernicious Kingdoms, Reliance on Reverse DNS Resolution for a Security-Critical Action from PLOVER, and DEPRECATED: Trusting Self-reported DNS Name from CLASP. All taxonomies focused closely on the use of reverse DNS for authentication of incoming requests.