Network Tools

Webscan – Browser-based Network Scanner And local-IP Detection

December 1, 2020
4 Min Read
Webscan - Browser-based Network Scanner And local-IP Detection

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webscan is a browser-based network IP scanner and local IP detector. It detects IPs bound to the user/victim by listening on an RTP data channel via WebRTC and looping back to the port across any live IPs, as well as discovering all live IP addresses on valid subnets by monitoring for immediate timeouts (TCP RST packets returned) from fetch() calls or hidden img tags pointed to valid subnets/IPs. Works on mobile and desktop across all major browsers and OS’s. Beta version is extensible to allow the addition of multiple techniqu es.

webscan takes advantage of the fact that non-responsive img tag sockets can be closed to prevent browser & network-based rate limiting by altering the src attribute to a non-socket URI (removing from DOM ironically does not close the socket), or by using fetch()’s signal support of the AbortController() interface.

try webscan live here
beta version here

by @SamyKamkar
released 2020/11/07
more fun projects at samy.pl

webscan works like so

  1. webscan first iterates through a list of common gateway IP addresses
  2. for each IP, use fetch() to make fake HTTP connection to http://common.gateway.ip:1337
  3. if a TCP RST returns, the fetch() promise will be rejected or img tag onerror will trigger before a timeout, indicating a live IP
  4. to prevent browser or network rate limiting, non-responsive fetch() sockets are closed via AbortController() signal while img-tags have the src redirected to non-socket URI, closing the socket
  5. when live gateway detected, step 1-3 reran for every IP on the subnet (e.g. 192.168.0.[1-255])
  6. a WebRTC data channel is opened on the browser, opening a random port on the victim machine
  7. for any IPs that are found alive on the subnet, a WebRTC data channel connection is made to that host
  8. if the WebRTC data channel is successful, we know we just established a connection to our own local IP

implementation

// wait for scan to finish
let scanResults = await webScanAll()
// or get callbacks when ips are found with a promise
let ipsToScan = undefined // scans all pre-defined networks if null
let scanPromise = webScanAll(
ipsToScan, // array. if undefined, scan major subnet gateways, then scan live subnets. supports wildcards
{
rtc: true, // use webrtc to detect local ips
logger: l => console.log(l), // logger callback
localCallback: function(ip) { console.log(`local ip callback: ${ip}`) },
networkCallback: function(ip) { console.log(`network ip callback: ${ip}`) },
}
)

returns

scanResults = {
  "local": ["192.168.0.109"], // local ip address
  "network": { // other hosts on the network and how fast they respond
    "192.168.0.1": 97,
    "192.168.0.2": 82,
    "192.168.0.100": 46,
    "192.168.0.109": 0,
    "192.168.0.117": 74,
    "192.168.0.113": 17,
    "192.168.0.112": 21,
    "192.168.0.114": 25,
    "192.168.0.116": 25,
    "192.168.0.115": 25,
    "192.168.0.105": 57,
    "192.168.0.107": 63,
    "192.168.0.103": 64,
    "192.168.0.108": 31
  }
}

Todo

  • use iframe to perform scans in blocks
    • when the frame is torn down, i assume this helps guarantee the connections are torn down
    • how do multiple iframes scanning multiple blocks work? perhaps this allows us to bypass browser connection rate limiting
  • support both fetch() and img as scanner cores (completed in beta)
    • Safari
      • note: img tag works really well in some browsers like Safari
      • caveat: changing the .src doesn’t seem to abort the connection
      • potential solution: see iframe note above
    • Chrome
      • caveat: chrome will not abort the connection if you remove the img from dom
      • solution: chrome will abort the connection of an img if you adjust the .src, this is great!
      • caveat: changing the img.src to ‘#’ makes another request to the same parent page
      • caveat: changing the img.src to ‘about:’ produces a warning in console, is there something else to use that won’t make a request?
  • use img timing as a local ip detection mechanism

Tested on

  • Chrome 87.0.4280.47 (macOS)
  • Edge 86.0.622.63 (Windows)
  • Firefox 82.0.2 (macOS)
  • Firefox 82.0.2 (Windows 10)
  • Safari 13.1.2 (macOS)
  • mobile Safari (iOS)
  • mobile Chrome (iOS)

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