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Intercepting iOS App Traffic with mitmproxy CLI & Web UI Guide

· 5 min read

Intercepting HTTP(S) traffic from a real iOS device is a powerful way to understand what your app (or any third‑party app like Medscape) is sending and receiving—without Xcode, without re‑signing, and without touching a simulator. In this guide, we’ll walk through both the command‑line interface (CLI) and the Web UI (mitmweb) methods for capturing, filtering, modifying, and exporting your mobile traffic.

📋 Prerequisites​

  • A Mac (or Linux) machine on the same Wi‑Fi network as your iOS device
  • Homebrew (macOS) or Python 3 & pip3
  • mitmproxy installed via Homebrew or pip3
  • Basic familiarity with terminal commands and iOS Settings

🔧 Installing mitmproxy​

Homebrew (macOS)​

brew install mitmproxy

pip3 (cross‑platform)​

pip3 install mitmproxy

This installs three binaries:

  • mitmproxy – interactive CLI (text UI)
  • mitmweb – browser‑based Web UI
  • mitmdump – headless, scriptable

Tip: Always keep mitmproxy updated (brew upgrade mitmproxy or pip3 install --upgrade mitmproxy).

🔐 Generating & Installing the mitmproxy CA Certificate​

mitmproxy uses a custom Certificate Authority (CA) to decrypt HTTPS.

  1. Run mitmweb (or mitmproxy) once to auto‑generate the CA:

    mitmweb --listen-port 8082 --listen-host 0.0.0.0 --web-port 8081
    # Ctrl+C to stop after you see "generated new CA at ~/.mitmproxy/mitmproxy-ca.pem"

  2. Serve the cert so your iOS device can download it:

    cd ~/.mitmproxy
    python3 -m http.server 8000

  3. On your iOS device’s Safari, visit:

    http://<YOUR_MAC_IP>:8000/mitmproxy-ca-cert.pem

    – Tap Allow, then Close.

  4. Install & trust:

    • Settings → General → VPN & Device Management → tap “mitmproxy” profile → Install.
    • Settings → General → About → Certificate Trust Settings → toggle mitmproxy ON.

Pro tip: If you later rotate mitmproxy’s CA, remove the old profile on iOS first to prevent conflicts.

📶 Configuring Your iOS Device Proxy​

  1. Settings → Wi‑Fi → (ℹ︎) your network → Configure Proxy → Manual
  2. Server: your Mac’s LAN IP (e.g. 192.168.1.42)
  3. Port: 8082
  4. Save.

Now all HTTP/S traffic on that SSID flows through mitmproxy.

Hint: If you roam off Wi‑Fi (e.g. to Cellular), you’ll lose the proxy. Keep an eye on your status bar.

🖥️ Using the CLI: mitmproxy​

For quick inspection or scripting, the CLI TUI is lightning fast.

Launch​

mitmproxy --listen-port 8082 --listen-host 0.0.0.0

Basic Navigation​

  • ↑/↓ – scroll through flows
  • Enter – open flow detail (headers & body)
  • e – set an edit breakpoint on this flow
  • f – filter (type filter expression, e.g. ~u containerBeacon)
  • q – quit

Filtering Examples​

  • Container beacon endpoint:

    ~u containerBeacon

  • ID5 SDK script load:

    ~u id5-sync.com

  • Combine filters:

    (~u containerBeacon) or (~u id5-sync.com)

Intercept & Modify​

  • Press e on a flow → reproduce on your device → the flow will pause.
  • Edit request headers/body inline → press a to accept & continue or d to drop.

CLI Tip: Pipe mitmproxy logs to a file for offline debugging:

mitmproxy --listen-port 8082 --listen-host 0.0.0.0 --mode regular@8082 2>&1 | tee mitmproxy.log

🌐 Using the Web UI: mitmweb​

The Web UI offers a user‑friendly dashboard in your browser.

Launch​

mitmweb --listen-host 0.0.0.0 --listen-port 8082 --web-port 8081
  • Proxy on 0.0.0.0:8082
  • UI at http://localhost:8081/ (or http://<YOUR_MAC_IP>:8081/)

Key Features​

  1. Live Flows List – real‑time streaming of requests/responses.
  2. Filter Box – same filter syntax as CLI (~u, ~h, ~q, etc.).
  3. Flow Detail Pane – click any request to see Request / Response / Timeline.
  4. Intercept Toggle – a checkbox in the leftmost column; click to pause flows.
  5. Copy as cURL – right‑click on any flow for easy replay.

Filter Examples​

~u containerBeacon or ~u id5-sync.com or ~u your-rple-host

Exporting & Auditing​

  • File → Export HTTP Archive… → choose “Filtered flows” → save .har for team reviews.
  • Share HARs or screenshots of the Web UI for clear “no Xcode” evidence.

Web UI Tip: Use your browser’s DevTools to style the Web UI: larger fonts or dark mode via user CSS!1

🔄 Scripting with Add‑ons​

Want to automate logging or custom breakpoints? Write a small Python addon.

# log_beacons.pyrom mitmproxy import http, ctx

def request(flow: http.HTTPFlow):
    url = flow.request.pretty_url
    if "containerBeacon" in url or "id5-sync.com" in url:
        ctx.log.info(f"[MITM] {flow.request.method} → {url}")
        ctx.log.info(flow.request.get_text())

Launch with:

mitmproxy -s log_beacons.py --listen-port 8082 --listen-host 0.0.0.0

Logs appear in your terminal or Web UI Log panel.

🚀 Tips & Tricks​

  • Port conflicts: If address already in use occurs, find and kill the process on that port (lsof -iTCP:8082 | grep LISTEN). Or select a new port with --listen-port.
  • Remember to trust the CA after rotation or OS updates can revoke profiles.
  • Selective bypass: Exclude domains (e.g. App Store) by adding a bypass rule: --anticache or --no-upstream-cert to speed up non‑essential traffic.
  • Device certificates: iOS 14+ may require cert installation via MDM for full trust.

🎯 Conclusion​

With mitmproxy (CLI or Web UI), you gain complete visibility into real-device HTTPS traffic—no Xcode entanglements required. Whether you’re auditing Medscape’s container beacons, verifying ID5 SDK loads, or debugging custom RPLE endpoints, this guide equips you to:

  • Install and trust the CA certificate
  • Configure your iOS device proxy
  • Capture, filter, and inspect flows via CLI or Web UI
  • Intercept, modify, and log requests on the fly
  • Export HAR files for audit and collaboration

Happy sniffing, and may your beacons always fire correctly!

Footnotes​

  1. For Chrome, install an extension like “Stylus” and apply a dark theme to localhost:8081. ↩