How to get DNS rewrite script working?

[natevw]

I am new to mitmproxy and trying to figure out how to configure custom behavior. I see a variety of scripts around, for example I found https://gist.github.com/clouedoc/818e05949717d9cfab9e709b9b05fe7a/91c2711864f39af60ffe547c8020a4a13564ca63 which I simplified down to:

tgt_host = "ipcalf.com"

class OverrideDNS:
    def dns_request(self, flow: mitmproxy.dns.DNSFlow):
        if any(q.name == tgt_host for q in flow.request.questions):
            flow.response = flow.request.succeed(
                [
                    dns.ResourceRecord.A(
                        tgt_host, IPv4Address("10.0.2.2"), ttl=10
                    )
                ]
            )
            logging.info("Overwrite DNS response")
            flow.comment = "Overwrote by OverrideAP"
            flow.marked = ":black_nib:"

addons = [OverrideDNS()]

Tucked into https://docs.mitmproxy.org/stable/addons/overview/ I see there is a -s option (short for --scripts) to pass the script. So combining that with just the basic mode stuff I'd already figured out, I have something like:

mkdir -p ~/.mitmproxy
cp ~/Downloads/custom-dns.py ~/.mitmproxy/custom-dns.py
mitmPw=letmein
container run -d --name mitm --rm \
  -v ~/.mitmproxy:/home/mitmproxy/.mitmproxy \
  -p 8080:8080 -p 127.0.0.1:8081:8081 \
  docker.io/mitmproxy/mitmproxy mitmweb \
  --web-host 0.0.0.0 \
  --set web_password=${mitmPw} \
  -s /home/mitmproxy/.mitmproxy/custom-dns.py \
  --mode=reverse:https://ipcalf.com \
  --mode=dns
mitmIp=$(container inspect mitm | jq -r '.[0].networks[0].ipv4Address' | cut -d / -f 1)
open "http://${mitmIp}:8081?token=${mitmPw}"

but when I follow that up with dig @$mitmIp ipcalf.com I still just get the original IP address. (I can't just modify /etc/hosts in the mitm container itself, which does change the IP result, but also breaks the later upstream connection I'm trying to make to the same host.)

Going into the container via container exec -it -e mitmIp="$mitmIp" mitm /bin/bash and inspecting:

mitmPkg=$(dirname $(python -c 'import mitmproxy; print(mitmproxy.__file__)'))
grep -C 2 ScriptLoader "${mitmPkg}/addons/__init__.py"

I see that it does have the new ordering merged via #7685 (script.ScriptLoader() before dns_resolver.DnsResolver(). I do see it mention loading the script when it starts up but it doesn't annotate the flow (or of course modify the result).

[natevw]

Aaaaah, was so close! The script itself was simply incomplete/buggy.

Found in the logs (via http://${mitmIp}:8081/#/flows?e=true) a Python error like:

Traceback (most recent call last):
File "/home/mitmproxy/.mitmproxy/custom-dns.py", line 8, in dns_request
dns.ResourceRecord.A(
^^^
NameError: name 'dns' is not defined

And proceeded from there. Basically the example I found was missing a whole bunch of imports. The official example https://docs.mitmproxy.org/stable/addons/examples/#dns-simple which I've now found would have been a better starting point. Combining what I'd started with, with what it needed to be as:

from ipaddress import ip_address
from mitmproxy import dns
import logging

target_domain = "ipcalf.com"
fake_record = "10.0.0.42"

def dns_request(flow: dns.DNSFlow) -> None:
    q = flow.request.question
    if q.name == target_domain and q.type == dns.types.A:
        logging.info(f"Spoofing record for {q.name}...")
        flow.response = flow.request.succeed([
            dns.ResourceRecord.A(
                name=q.name,
                ip=ip_address(fake_record),
            )
        ])

and it's working! 🎊

I guess I'll close this since I have my answer, but hopefully a more completely worked example (which should largely work with docker/podman in place of Apple's container albeit with some IP address fixup…) will be helpful to other newcomers as well. The CLI interface isn't well documented on the website but via --help and piecing together various clues was able to get this working in not too much time — thanks to the devs for their work on this system!

[Lidiamaria11]

Hello good morning.... I am Lidia by my name, I could like to help if you need any assistant.