[Security] Mitigate DNS rebinding flaw

[feross]

Mitigate the WebTorrent DNS rebinding flaw disclosed in HackerOne. Low security/privacy risk.

Original issue: brave/browser-laptop#12616
Original Brave PR: brave/browser-laptop#13844
Original WebTorrent PR: webtorrent/webtorrent#1260
Fixed WebTorrent PR: webtorrent/webtorrent#1678

The fix is already published in webtorrent@0.105.2. We should update to this version.

[feross]

Test Plan

1. Go to https://webtorrent.io/free-torrents
2. Select Sintel (magnet link)
3. Start the download
4. Hover your mouse over the download link (the downward-facing arrow) and observe the link's port number. It should be something like e.g. 58630.
5. Run the following command in Terminal (tested on Mac): cat <(echo -en 'GET / HTTP/1.1\r\nHost: attacker.com\r\n\r\n') - | nc localhost 58630. Note: be sure to replace 58630 in the command with the actual port number you observed in Step 4.
6. The command should hang without outputting anything to Terminal at all. If you see an HTTP response or HTML, then this is broken. Nothing should be output from the command.

[diracdeltas]

hackerone issue: https://hackerone.com/reports/663729

[kjozwiak]

Verification PASSED on macOS 10.14.6 x64 using the following build:

Brave	0.69.126 Chromium: 77.0.3865.65 (Official Build) (64-bit)
Revision	87a331a3169cab563505fb44011058b904011ba1-refs/branch-heads/3865@{#726}
OS	macOS Version 10.14.6 (Build 18G95)

• Verified STR outlined under [Security] Mitigate DNS rebinding flaw #5460 (comment)

Verification passed on

Brave	0.69.127 Chromium: 77.0.3865.75 (Official Build) (64-bit)
Revision	201e747d032611c5f2785cae06e894cf85be7f8a-refs/branch-heads/3865@{#776}
OS	Ubuntu 18.04 LTS

• Verified STR outlined under [Security] Mitigate DNS rebinding flaw #5460 (comment)
  

Verification passed on

Brave	0.69.129 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

• Verified STR outlined under [Security] Mitigate DNS rebinding flaw #5460 (comment)
  

[GeetaSarvadnya]

@feross @yrliou what is the command for windows? I have used the below command in windows and I have got command not found message.

[yrliou]

Talked to @GeetaSarvadnya through DM about testing on Windows, note here for future references.
On Windows, we could install nmap from https://nmap.org/ncat/ which includes ncat.
When testing, change to the installation folder, such as c\Program Files (x86)\Nmap, and run
cat <(echo -en 'GET / HTTP/1.1\r\nHost: attacker.com\r\n\r\n') - | ./ncat.exe localhost 49976 (Replace port with the result of previous step.)
This command is tested using MINGW64, might need a little tweak if you are using other tools.