Exploit that gives remote access affects ~200 million cable modems

Hundreds of millions of cable modems are susceptible to important takeover assaults by hackers halfway close to the earth, scientists claimed.

The assaults get the job done by luring susceptible end users to websites that serve destructive JavaScript code which is surreptitiously hosted on the web site or concealed within of destructive advertisements, scientists from Denmark-based mostly safety organization Lyrebirds claimed in a report and accompanying website. The JavaScript then opens a websocket relationship to the susceptible cable modem and exploits a buffer overflow vulnerability in the spectrum analyzer, a modest server that detects interference and other connectivity difficulties in a host of modems from various makers. From there, distant attackers can acquire comprehensive command about the modems, permitting them to adjust DNS configurations, make the modem aspect of a botnet, and have out a range of other nefarious steps.

Cable Haunt, as the scientists have named their evidence-of-thought exploit, is known to get the job done on various firmware variations of the adhering to cable modems:

  • Sagemcom F@st 3890
  • Sagemcom F@st 3686
  • Technicolor TC7230
  • Netgear C6250EMR
  • Netgear CG3700EMR

The exploit might also get the job done in opposition to the Compal 7284E and Compal 7486E. For the reason that the spectrum analyzer server is current in other cable modems, the exploit is probable to get the job done on other styles as effectively. Lyrebirds’ evidence-of-thought attack will work reliably in opposition to the Technicolor TC7230 and the Sagemcom F@st 8690. With tweaks, the attack code will get the job done on other styles stated as susceptible. The vulnerability is tracked as CVE-2019-19494. A far more unique vulnerability concentrating on only the technicolor TC7230 modem is indexed as CVE-2019-19495.

Entire command

“The vulnerability enables distant attackers to acquire comprehensive command of a cable modem, by way of an endpoint on the modem,” Lyrebirds scientists wrote. “Your cable modem is in charge of the World-wide-web targeted traffic for all devices on the network. Cable Haunt may hence be exploited to intercept personal messages, redirect targeted traffic, or participat[e] in botnets.”

There are at the very least two approaches the exploit can acquire distant entry, meaning it can be exploited about the World-wide-web by an attacker who is outside the house the neighborhood network.

The to start with and most clear-cut way is to serve destructive JavaScript that triggers the browser to connect to the modem. Normally, a system named cross-origin source sharing helps prevent a World-wide-web application from a person origin (these types of as destructive.example.com) from performing on a unique origin (these types of as, the deal with used by most or all of the susceptible modems).

Websockets, nonetheless, are not protected by CORS, as the system is typically named. As a final result, the modems will accept the distant JavaScript, thereby permitting attackers to achieve the endpoint and serve it code. While Cabe Haunt accesses modems by way of a browser, the attack can arrive from any position wherever operating code can achieve an IP on the neighborhood network.

Rebinding assaults, ROP, and far more

The attack won’t get the job done when susceptible targets use Firefox, simply because the websocket used by that browser is just not suitable with the websocket used by the spectrum analyzer. Attackers can nonetheless have out their distant attack by using JavaScript that carries out what’s known as a DNS rebinding attack. To bypass the same origin policy—a restriction that helps prevent code served from a person domain from executing on a unique domain—the rebinding attack manipulates DNS tables within the neighborhood network. For the reason that the attack site’s domain deal with is mapped to the IP of the susceptible modem, the JavaScript will execute the attack code efficiently.

Other than the buffer overflow, the attack is attainable simply because of known default credentials used to execute code on modems. These default credentials are just extra to the URL used by the attack code, e.g.: http://username:password@destructive.example.com. Lyrebirds cofounder Kasper Tendrup explained to me he believes there are other solutions for making the attack get the job done remotely.

The evidence-of-thought exploit uses other intelligent tricks to get the job done. For the reason that of the memory structure of the MIPS assembly language that operates the spectrum analyzer, the attack code have to know the precise memory deal with of the susceptible code. (Normally, a buffer overflow exploit would be prepared specifically to the memory stack.) To bypass the restriction posed by this memory structure, Cable Haunt uses return oriented programming to move amongst pre-current parts of code and then generate a patchwork of current code.

After attackers exploit the vulnerability, they send instructions to the modem’s telnet server to put in a reverse shell. From there, attackers can do all forms of issues, together with transforming the DNS configurations, installing wholly new firmware, making the modem participate in a botnet, and checking unencrypted data that passes by way of the modem.

200 million modems

The Lyrebirds analysis implies that Cable Haunt will work in opposition to as several as 200 million modems in Europe by itself. The attack might get the job done in opposition to a greater range of modems deployed throughout the rest of the earth. Determining if a modem not on the Lyrebirds checklist is susceptible is just not easy for normal end users simply because it involves them to operate this PoC code in opposition to the product. Detecting hacked modems is also rough because there are a range of approaches to mask the infection after attackers acquire root entry on a product.

Cable Haunt is a serious vulnerability that deserves to be patched shortly. The most probable way to target end users would be to send emails to end users of ISPs that are known to supply a susceptible modem to end users. The electronic mail would instruct end users to take a look at web pages that serve the attack.

Makers of the modems known to be susceptible didn’t instantly answer to emails looking for remark for this publish. Worried cable modem end users really should check out with either the maker of the product or the ISP that issued it.

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