Cable Modems Vulnerable to Cable Haunt Vulnerabilities

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TL;DR
If you are cautious with the links you click and when processing your email, you will likely not be vulnerable to these flaws. If you use a cable modem for your internet connection, you should check if your modem is vulnerable and follow the step “What should I do” mentioned below.
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In mid-January it was discovered the firmware (defined) of many internet service provider (ISP) modems (specifically combined modems and routers in the same device) was vulnerable to remote takeover by attackers. These vulnerabilities have been named Cable Haunt as an easier to remember reference.

How widespread are the affected modems?
At the least the following manufacturers are affected with up to 200 million vulnerable modems mainly based in Europe but other regions e.g. North America are also affected. Please see also the FAQ “Am I Affected” on the Cable Haunt website.

Arris
COMPAL
Netgear
Sagemcom
Technicolor

Other brands of modems confirmed by the wider community as being vulnerable are:

Cisco EPC3928AD
Cisco/Technicolor DPC3216
Humax HGB10R-02
SMC Electronics SMC D3-CCR-v2
Zoom 5370
Virgin Media’s Super Hub 3 and 4 do not appear to be vulnerable.

How serious are these vulnerabilities?
While the vulnerabilities are serious in their impact, namely complete remote compromise of the device, how an attacker could exploit the vulnerabilities to achieve that outcome is not trivial. As per the researchers:

“This could be exploited by an attacker if you visit a malicious website or if they embed the code, for instance in an advert, on a trusted website. It is important to point out that this is not the only attack vector that can be employed, vulnerable mail-clients, exploited IoT devices, public networks etc. are also viable attack vectors”.

Summary of the Technical Aspects of these vulnerabilities
The vulnerability designated formally as CVE-2019-19494 is a buffer overflow (defined) that if exploited could allow remote code execution (defined: the ability for an attacker to remotely carry out any action of their choice on your device) with kernel level (defined) privileges by using JavaScript (defined) within your web browser. The buffer overflow can be exploited using (according to the researchers: “a carefully crafted message the modem can be manipulated to execute arbitrary code specified by a remote attacker”.

An important aspect of the above described exploit is that while the attack is a remote attack (using a victim’s web browser) it results in the local compromise of the modems spectrum analyser. Linked to this; a DNS re-bind attack (defined) can be used to enable an attacker the ability to access the compromised spectrum analyser. The result of the above exploits provides the attackers with (according to the researchers): “full remote control over the entire unit, and all the traffic that flows through it, while being invisible for both the user and ISP,”. This capability could be used to:

  1. Intercept private messages
  2. Redirect traffic
  3. Add the modems to botnets
  4. Replace the devices firmware
  5. Instruct the device to ignore remote system updates (which could be used to patch the vulnerabilities, complicating the resolution of a compromised device by its legitimate owner/user)

How can I protect my organisation or myself from these vulnerabilities?\
For in-depth answers from the researchers to answer this question in the context of an internet service provider (ISP), the user of the modem (e.g. within a small business), as an individual or a security researcher, please see the question “What Should I do” on the dedicated Cable Haunt website:

https://cablehaunt.com/

According to Graham Cluley: “Some ISPs in Scandinavia appear to have remotely patched the cable modems of their customers, but others have some catching up to do it seems.
If your cable modem contains a Broadcom chipset you might want to contact your ISP and ask them what they’re doing about this”.

Thank you.

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My sincere thanks to the Cable Haunt researchers Alexander Dalsgaard Krog (Lyrebirds), Jens Hegner Stærmose (Lyrebirds), Kasper Kohsel Terndrup (Lyrebirds) and Simon Vandel Sillesen (Independent) as well as Graham Cluley for the excellent information which this blog post is built upon.

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