Watch How Easy It Is to Hack the Future of Texting
2019-12-09 23:24

Ask practically any phone carrier, and they'll tell you that the future of smartphone features from texting to video calls is a protocol called Rich Communication Services. Think of RCS as the successor to SMS, an answer to iMessage that can also handle phone and video calls. Last month, Google announced it would begin rolling RCS out to its Messages app in all US Android phones. It's easy to imagine a near-future where RCS is the default for a billion people or more. But when security researchers looked under the hood, they found the way carriers and Google have implemented the protocol creates a basket of worrisome vulnerabilities.

几乎所有的手机运营商都会告诉你,从短信服务到视频通话等智能手机的各类功能将会被一种名为富通信服务(Rich Communication Services)的协议所取代。富通信服务可以说是从其前身短讯服务演变而来的,后者是针对iMessage所构想的一种解决方案,同样可以用于处理普通电话和视频电话。上个月,谷歌宣布推出的富通信服务将面向全美市场所有安卓手机的短信应用。不难想象,在不久的将来,RCS将成为10亿人口甚至更大范围的默认选择。但当安全研究人员深入调查后,他们发现运营商和谷歌达成协议的途径存在一系列令人担忧的漏洞。

At the Black Hat security conference in London on Tuesday, German security consultancy SRLabs demonstrated a collection of problems in how RCS is implemented by both phone carriers and Google in modern Android phones. Those implementation flaws, the researchers say, could allow texts and calls to be intercepted, spoofed, or altered at will, in some cases by a hacker merely sitting on the same Wi-Fi network and using relatively simple tricks. SRLabs previously described those flaws at the DeepSec security conference in Vienna last week, and at Black Hat also showed how those RCS hijacking attacks would work in videos like the one below:

在周二于伦敦举行的黑帽安全会议上,德国安全咨询公司SRLabs揭发了手机运营商和谷歌在现代安卓手机中应用RCS所导致的一系列问题。研究人员表示,实施过程中的这些漏洞可能会使得短信和电话被随意拦截、欺骗或篡改,而在某些情况下,黑客们只需要在同一个Wi-Fi网络下,使用相对简单的技巧就能发现这些漏洞。SRLabs之前在上周于维也纳召开的DeepSec安全会议上阐述了这些漏洞,在Black Hat上也通过视频展示了这些RCS劫持攻击的操作流程,如下图所示:

SRLabs founder Karsten Nohl, a researcher with a track record of exposing security flaws in telephony systems, argues that RCS is in many ways no better than SS7, the decades-old phone system carriers still used for calling and texting, which has long been known to be vulnerable to interception and spoofing attacks. While using end-to-end encrypted internet-based tools like iMessage and WhatsApp obviates many of those of SS7 issues, Nohl says that flawed implementations of RCS make it not much safer than the SMS system it hopes to replace.


"You're going to be more vulnerable to hackers because your network decided to activate RCS," says Nohl. "RCS gives us the capability to read your text messages and listen to your calls. That's a capability that we had with SS7, but SS7 is a protocol from the '80s. Now some of these issues are being reintroduced in a modern protocol, and with support from Google."


The RCS rollout still has a ways to go, and will continue to be a patchwork even with Google's backing. Some Android manufacturers use proprietary messaging apps as the default rather than the stock Messages app, and most carriers push their own versions as well. The iPhone doesn't support it at all, and Apple has given no indication that it will. But as RCS rolls out more broadly, its security issues merit attention—especially since it's those implementations that create the problems in the first place.


The SRLabs videos demonstrate a grab bag of different techniques to exploit RCS problems, all of which are caused by either Google's or one of the phone carriers' flawed implementations. The video above, for instance, shows that once a phone has authenticated itself to a carrier's RCS server with its unique credentials, the server uses the phone's IP address and phone number as a kind of identifier going forward. That means an attacker who knows the victim's phone number and who is on the same Wi-Fi network—anyone from a coworker in the same corporate office to someone at the neighboring table at Starbucks—can potentially use that number and IP address to impersonate them.


Using a different technique, the researchers showed how an Android phone using RCS can be vulnerable to a man-in-the-middle attack. Whether it's a hacker controlling a malicious Wi-Fi network or an ISP or nation-state spies with access to an ISP's servers, an attacker can alter the domain name system request that the phone uses to find the RCS server that acts as the relay between senders and recipients of a message. SRLabs found that while Android's RCS-enabled messaging app checks to see if the server the phone is connecting to has a valid TLS certificate—in the same way your browser checks the validity of an HTTPS website—it will accept any valid certificate, even for the attacker's server.

研究人员使用了一种不同的技术,展示了使用RCS的Android手机如何容易受到中间人攻击。不管是黑客控制恶意wi - fi网络或ISP或民族国家间谍与ISP的服务器,攻击者可以改变手机用来查找在发送者和接收者之间传达信息的RCS服务器的域名系统请求。SRLabs发现,当Android的RCS消息应用程序检查手机连接的服务器是否具备合法的TLS证书时,它对任何合法证书都来者不拒,甚至是攻击者的服务器。

It's like a security guard who only checks if someone's ID matches their face, rather than if their name is on the approved list in the first place. "It's a really stupid mistake," adds Nohl.


The result is that the man-in-the-middle can intercept and alter messages at will, as shown in this video:


Another attack takes advantage of a flaw in the initial setup for RCS devices. When a phone is first registered in the RCS system, it downloads a configuration file that contains the device's credentials. But to identify itself to the server and download that configuration file, a device only needs to have the IP address the carrier believes is meant to be associated with that device's phone number. Nohl points out, however, that any malicious app that ends up on a phone—even without special app permissions in Android—can reach out from the same IP address, steal the device's unique RCS credentials, and start impersonating it, as shown in the video below. That configuration file attack can be used even against someone who has never enabled RCS on their phone, Nohl points out.


In some cases, carriers try to guard against that attack by sending a one-time code to the user's device that they have to enter. But SRLabs found that some carriers failed to limit the number of tries at guessing that code; a hacker can try every possible number in just five minutes. "In five minutes we have your configuration file, and forever after we can listen to all your phone calls and read all your texts," Nohl says.


All of these attacks become even more serious when RCS messaging is used as a second factor in two-factor authentication. In that case, RCS interception could allow hackers to steal one-time codes and gain access to other, even more sensitive accounts like email, as shown in this video:


When WIRED reached out to the GSM Association phone carrier industry group and Google, the company responded with a statement thanking the researchers but arguing that "many of these issues have already been addressed"—it declined to say which ones—"and as part of our close collaboration with the ecosystem, we're actively advising partners as they resolve the remaining issues." The GSMA claimed that it already knew of the issues SRLabs highlighted, and that "countermeasures and mitigation actions are available" for carriers to fix their RCS flaws. Nohl countered that those fixes haven't been implemented yet for any of the issues SRLabs presented on at Black Hat.


The GSMA further argued that SRLabs had pointed out problems with the implementation of the RCS standard, rather than the standard itself. "The findings highlight issues with some RCS implementations but not every deployment, or the RCS specifications themselves, are impacted," the GSMA statement reads.


Nohl argues, however, that the existence of so many flaws in the standard's implementations is in fact a problem with the standard. "If you put out a new technology for a billion people, you should define the whole security concept. Instead RCS leaves a lot undefined, and telcos make a lot of individual mistakes when trying to implement this standard," Nohl says. "This is a technology being introduced quietly to over a billion people already. And it exposes them to threats they didn't have to worry about previously."


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