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BitTorrent users beware: Flaw lets hackers control your computer

There’s a vicious debility in the widely used Transmission BitTorrent app that allows websites to govern antagonistic code on some users’ computers. That’s according to a researcher with Google’s Project Zero disadvantage stating team, who also warns that other BitTorrent clients are likely likewise susceptible.

Researcher Tavis Ormandy published the proof-of-concept attack code last week, along with a minute outline of the underlying disadvantage it exploited. Normally, Project Zero withholds announcement of such sum for 90 days or until the developer has expelled a fix. In this case, however, Ormandy’s private report to Transmission enclosed a patch that totally firm the vulnerability. The researcher went forward and disclosed the disadvantage last Tuesday—only 40 days after the initial report—because Transmission developers had nonetheless to request it. Ormandy pronounced the announcement would concede Ubuntu and other downstream projects to exclusively install the fix.

“I’m anticipating it frustrating that the Transmission developers are not responding on their private confidence list,” Ormandy wrote in Tuesday’s open report. “I suggested moving this into the open so that distributions can request the patch independently.”

A Transmission growth central told Ars that he approaching an central fix to be expelled “ASAP” but was not specific. He pronounced the disadvantage was benefaction only when users enabled remote entrance and infirm cue protection. He pronounced people who run the unpatched chronicle of Transmission as a daemon should safeguard they have enabled cue protection.


DNS rebinding strikes again

Ormandy’s proof-of-concept attack exploits a Transmission duty that allows users to control the BitTorrent app with their Web browser. The researcher pronounced many people don’t capacitate cue insurance since they assume the JSON RPC interface can only be tranquil by someone with earthy entrance to the mechanism using Transmission. Using a hacking technique famous as domain name complement rebinding, Ormandy devised a way that the Transmission interface can be remotely tranquil when a exposed user visits a antagonistic site. He pronounced he reliable his feat works on Chrome and Firefox on Windows and Linux and that he expects other platforms and browsers are also affected.

Attackers can feat the smirch by formulating a DNS name they are certified to promulgate with and then making it solve to the localhost name of the exposed computer. In a apart posting edition the patch, Ormandy wrote:

  1. A user visits http://attacker.com, which has an iframe to a subdomain the assailant controls.
  2. The assailant configures their DNS server to respond alternately with and (an residence they control) with a very low TTL.
  3. When the browser resolves to, they offer HTML that waits for the DNS entrance to end (or force it to end by flooding the cache with lookups), then they have permission to review and set headers.

Among the things an assailant can do is change the Torrent download office to the user’s home directory. The assailant could then authority Transmission to download a Torrent called “.bashrc” which would automatically be executed the next time the user non-stop a whack shell. Attackers could also remotely reconfigure Transmission to run any authority of their selecting after a download has completed. Ormandy pronounced the feat is of “relatively low complexity, which is since I’m fervent to make certain everybody is patched.”

In a tweet, Ormandy pronounced the disadvantage was the “first of a few remote code execution flaws in several renouned swell clients.” He didn’t name the other apps since the 90-day Window hasn’t sealed yet.

While last week’s avowal has the many evident consequences for Transmission users, its lessons about the dangers of DNS rebinding are broadly germane to people using a far-reaching operation of apps.

“I frequently confront users who don’t accept that websites can entrance services on localhost or their intranet,” Ormandy wrote. “These users know that services firm to localhost are only permitted to program using on the internal appurtenance and that their browser is using on the internal machine—but somehow trust that accessing a website ‘transfers’ execution somewhere else. It doesn’t work like that, but this is a common source of confusion.”

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