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.)
CWE-350 Variant Draft
Reliance on Reverse DNS Resolution for a Security-Critical Action
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…
Definition
What is CWE-350?
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.
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.
Real-world impact
Real-world CVEs caused by CWE-350
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Does not do double-reverse lookup to prevent DNS spoofing.
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Does not verify reverse-resolved hostnames in DNS.
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Authentication bypass using spoofed reverse-resolved DNS hostnames.
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Authentication bypass using spoofed reverse-resolved DNS hostnames.
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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.
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Reverse DNS lookup used to spoof trusted content in intermediary.
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Product records the reverse DNS name of a visitor in the logs, allowing spoofing and resultant XSS.
How attackers exploit it
Step-by-step attacker path
- 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.
- 2
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.
- 3
In these examples, a connection is established if a request is made by a trusted host.
- 4
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.
Vulnerable code example
Vulnerable C
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.
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;
} Secure code example
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist
How to prevent CWE-350
- Architecture and Design Use other means of identity verification that cannot be simply spoofed. Possibilities include a username/password or certificate.
- Implementation Perform proper forward and reverse DNS lookups to detect DNS spoofing.
Detection signals
How to detect CWE-350
Plexicus auto-detects CWE-350 and opens a fix PR in under 60 seconds.
Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.
Frequently asked questions What is CWE-350?
How serious is CWE-350?
What languages or platforms are affected by CWE-350?
How can I prevent CWE-350?
How does Plexicus detect and fix CWE-350?
Where can I learn more about CWE-350?
Frequently asked questions
What is CWE-350?
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.
How serious is CWE-350?
MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.
What languages or platforms are affected by CWE-350?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent CWE-350?
Use other means of identity verification that cannot be simply spoofed. Possibilities include a username/password or certificate. Perform proper forward and reverse DNS lookups to detect DNS spoofing.
How does Plexicus detect and fix CWE-350?
Plexicus's SAST engine matches the data-flow signature for CWE-350 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-350?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/350.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-350
CWE-290 Parent
Authentication Bypass by Spoofing
This weakness occurs when an application's authentication system can be tricked into accepting forged or manipulated credentials, allowing…
CWE-291 Sibling
Reliance on IP Address for Authentication
This vulnerability occurs when a system uses a client's IP address as the sole or primary method to verify their identity.
CWE-293 Sibling
Using Referer Field for Authentication
This vulnerability occurs when a web application uses the HTTP Referer header as a sole or primary method for authentication or…
CWE-923 Can precede
Improper Restriction of Communication Channel to Intended Endpoints
This vulnerability occurs when a system opens a communication channel for a sensitive task but fails to properly verify that it's actually…
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