How 1-Time Passcodes Became a Corporate Liability

Phishers are enjoying remarkable success using text messages to steal remote access credentials and one-time passcodes from employees at some of the world’s largest technology companies and customer support firms. A recent spate of SMS phishing attacks from one cybercriminal group has spawned a flurry of breach disclosures from affected companies, which are all struggling to combat the same lingering security threat: The ability of scammers to interact directly with employees through their mobile devices.

In mid-June 2022, a flood of SMS phishing messages began targeting employees at commercial staffing firms that provide customer support and outsourcing to thousands of companies. The missives asked users to click a link and log in at a phishing page that mimicked their employer’s Okta authentication page. Those who submitted credentials were then prompted to provide the one-time password needed for multi-factor authentication.

The phishers behind this scheme used newly-registered domains that often included the name of the target company, and sent text messages urging employees to click on links to these domains to view information about a pending change in their work schedule.

The phishing sites leveraged a Telegram instant message bot to forward any submitted credentials in real-time, allowing the attackers to use the phished username, password and one-time code to log in as that employee at the real employer website. But because of the way the bot was configured, it was possible for security researchers to capture the information being sent by victims to the public Telegram server.

This data trove was first reported by security researchers at Singapore-based Group-IB, which dubbed the campaign “0ktapus” for the attackers targeting organizations using identity management tools from Okta.com.

“This case is of interest because despite using low-skill methods it was able to compromise a large number of well-known organizations,” Group-IB wrote. “Furthermore, once the attackers compromised an organization they were quickly able to pivot and launch subsequent supply chain attacks, indicating that the attack was planned carefully in advance.”

It’s not clear how many of these phishing text messages were sent out, but the Telegram bot data reviewed by KrebsOnSecurity shows they generated nearly 10,000 replies over approximately two months of sporadic SMS phishing attacks targeting more than a hundred companies.

A great many responses came from those who were apparently wise to the scheme, as evidenced by the hundreds of hostile replies that included profanity or insults aimed at the phishers: The very first reply recorded in the Telegram bot data came from one such employee, who responded with the username “havefuninjail.”

Still, thousands replied with what appear to be legitimate credentials — many of them including one-time codes needed for multi-factor authentication. On July 20, the attackers turned their sights on internet infrastructure giant Cloudflare.com, and the intercepted credentials show at least three employees fell for the scam.

In a blog post earlier this month, Cloudflare said it detected the account takeovers and that no Cloudflare systems were compromised. Cloudflare said it does not rely on one-time passcodes as a second factor, so there was nothing to provide to the attackers. But Cloudflare said it wanted to call attention to the phishing attacks because they would probably work against most other companies.

“This was a sophisticated attack targeting employees and systems in such a way that we believe most organizations would be likely to be breached,” Cloudflare CEO Matthew Prince wrote. “On July 20, 2022, the Cloudflare Security team received reports of employees receiving legitimate-looking text messages pointing to what appeared to be a Cloudflare Okta login page. The messages began at 2022-07-20 22:50 UTC. Over the course of less than 1 minute, at least 76 employees received text messages on their personal and work phones. Some messages were also sent to the employees family members.”

On three separate occasions, the phishers targeted employees at Twilio.com, a San Francisco based company that provides services for making and receiving text messages and phone calls. It’s unclear how many Twilio employees received the SMS phishes, but the data suggest at least four Twilio employees responded to a spate of SMS phishing attempts on July 27, Aug. 2, and Aug. 7.

On that last date, Twilio disclosed that on Aug. 4 it became aware of unauthorized access to information related to a limited number of Twilio customer accounts through a sophisticated social engineering attack designed to steal employee credentials.

“This broad based attack against our employee base succeeded in fooling some employees into providing their credentials,” Twilio said. “The attackers then used the stolen credentials to gain access to some of our internal systems, where they were able to access certain customer data.”

That “certain customer data” included information on roughly 1,900 users of the secure messaging app Signal, which relied on Twilio to provide phone number verification services. In its disclosure on the incident, Signal said that with their access to Twilio’s internal tools the attackers were able to re-register those users’ phone numbers to another device.

On Aug. 25, food delivery service DoorDash disclosed that a “sophisticated phishing attack” on a third-party vendor allowed attackers to gain access to some of DoorDash’s internal company tools. DoorDash said intruders stole information on a “small percentage” of users that have since been notified. TechCrunch reported last week that the incident was linked to the same phishing campaign that targeted Twilio.

This phishing gang apparently had great success targeting employees of all the major mobile wireless providers, but most especially T-Mobile. Between July 10 and July 16, dozens of T-Mobile employees fell for the phishing messages and provided their remote access credentials.

“Credential theft continues to be an ongoing issue in our industry as wireless providers are constantly battling bad actors that are focused on finding new ways to pursue illegal activities like this,” T-Mobile said in a statement. “Our tools and teams worked as designed to quickly identify and respond to this large-scale smishing attack earlier this year that targeted many companies. We continue to work to prevent these types of attacks and will continue to evolve and improve our approach.”

This same group saw hundreds of responses from employees at some of the largest customer support and staffing firms, including Teleperformanceusa.com, Sitel.com and Sykes.com. Teleperformance did not respond to requests for comment. KrebsOnSecurity did hear from Christopher Knauer, global chief security officer at Sitel Group, the customer support giant that recently acquired Sykes. Knauer said the attacks leveraged newly-registered domains and asked employees to approve upcoming changes to their work schedules.

Knauer said the attackers set up the phishing domains just minutes in advance of spamming links to those domains in phony SMS alerts to targeted employees. He said such tactics largely sidestep automated alerts generated by companies that monitor brand names for signs of new phishing domains being registered.

“They were using the domains as soon as they became available,” Knauer said. “The alerting services don’t often let you know until 24 hours after a domain has been registered.”

On July 28 and again on Aug. 7, several employees at email delivery firm Mailchimp provided their remote access credentials to this phishing group. According to an Aug. 12 blog post, the attackers used their access to Mailchimp employee accounts to steal data from 214 customers involved in cryptocurrency and finance.

On Aug. 15, the hosting company DigitalOcean published a blog post saying it had severed ties with MailChimp after its Mailchimp account was compromised. DigitalOcean said the MailChimp incident resulted in a “very small number” of DigitalOcean customers experiencing attempted compromises of their accounts through password resets.

According to interviews with multiple companies hit by the group, the attackers are mostly interested in stealing access to cryptocurrency, and to companies that manage communications with people interested in cryptocurrency investing. In an Aug. 3 blog post from email and SMS marketing firm Klaviyo.com, the company’s CEO recounted how the phishers gained access to the company’s internal tools, and used that to download information on 38 crypto-related accounts.

The ubiquity of mobile phones became a lifeline for many companies trying to manage their remote employees throughout the Coronavirus pandemic. But these same mobile devices are fast becoming a liability for organizations that use them for phishable forms of multi-factor authentication, such as one-time codes generated by a mobile app or delivered via SMS.

Because as we can see from the success of this phishing group, this type of data extraction is now being massively automated, and employee authentication compromises can quickly lead to security and privacy risks for the employer’s partners or for anyone in their supply chain.

Unfortunately, a great many companies still rely on SMS for employee multi-factor authentication. According to a report this year from Okta, 47 percent of workforce customers deploy SMS and voice factors for multi-factor authentication. That’s down from 53 percent that did so in 2018, Okta found.

Some companies (like Knauer’s Sitel) have taken to requiring that all remote access to internal networks be managed through work-issued laptops and/or mobile devices, which are loaded with custom profiles that can’t be accessed through other devices.

Others are moving away from SMS and one-time code apps and toward requiring employees to use physical FIDO multi-factor authentication devices such as security keys, which can neutralize phishing attacks because any stolen credentials can’t be used unless the phishers also have physical access to the user’s security key or mobile device.

This came in handy for Twitter, which announced last year that it was moving all of its employees to using security keys, and/or biometric authentication via their mobile device. The phishers’ Telegram bot reported that on June 16, 2022, five employees at Twitter gave away their work credentials. In response to questions from KrebsOnSecurity, Twitter confirmed several employees were relieved of their employee usernames and passwords, but that its security key requirement prevented the phishers from abusing that information.

Twitter accelerated its plans to improve employee authentication following the July 2020 security incident, wherein several employees were phished and relieved of credentials for Twitter’s internal tools. In that intrusion, the attackers used Twitter’s tools to hijack accounts for some of the world’s most recognizable public figures, executives and celebrities — forcing those accounts to tweet out links to bitcoin scams.

“Security keys can differentiate legitimate sites from malicious ones and block phishing attempts that SMS 2FA or one-time password (OTP) verification codes would not,” Twitter said in an Oct. 2021 post about the change. “To deploy security keys internally at Twitter, we migrated from a variety of phishable 2FA methods to using security keys as our only supported 2FA method on internal systems.”

Update, 6:02 p.m. ET: Clarified that Cloudflare does not rely on TOTP (one-time multi-factor authentication codes) as a second factor for employee authentication.

A Deep Dive Into the Residential Proxy Service ‘911’

For the past seven years, an online service known as 911 has sold access to hundreds of thousands of Microsoft Windows computers daily, allowing customers to route their Internet traffic through PCs in virtually any country or city around the globe — but predominantly in the United States. 911 says its network is made up entirely of users who voluntarily install its “free VPN” software. But new research shows the proxy service has a long history of purchasing installations via shady “pay-per-install” affiliate marketing schemes, some of which 911 operated on its own.

911[.]re is one of the original “residential proxy” networks, which allow someone to rent a residential IP address to use as a relay for his/her Internet communications, providing anonymity and the advantage of being perceived as a residential user surfing the web.

From a website’s perspective, the IP traffic of a residential proxy network user appears to originate from the rented residential IP address, not from the proxy service customer. These services can be used in a legitimate manner for several business purposes — such as price comparisons or sales intelligence — but they are massively abused for hiding cybercrime activity because they can make it difficult to trace malicious traffic to its original source.

Residential proxy services are often marketed to people seeking the ability to evade country-specific blocking by the major movie and media streaming providers. But some of them — like 911 — build their networks in part by offering “free VPN” or “free proxy” services that are powered by software which turns the user’s PC into a traffic relay for other users. In this scenario, users indeed get to use a free VPN service, but they are often unaware that doing so will turn their computer into a proxy that lets others use their Internet address to transact online.

Researchers at the University of Sherbrooke in Canada recently published an analysis of 911, and found there were roughly 120,000 PCs for rent via the service, with the largest number of them located in the United States.

“The 911[.]re network uses at least two free VPN services to lure its users to install a malware-like software that achieves persistence on the user’s computer,” the researchers wrote. “During the research we identified two free VPN services that [use] a subterfuge to lure users to install software that looks legitimate but makes them part of the network. These two software are currently unknown to most if not all antivirus companies.”

The researchers concluded that 911 is supported by a “mid scale botnet-like infrastructure that operates in several networks, such as corporate, government and critical infrastructure.” The Canadian team said they found many of the 911 nodes available for rent were situated within several major US-based universities and colleges, critical infrastructures such as clean water, defense contractors, law enforcement and government networks.

Highlighting the risk that 911 nodes could pose to internal corporate networks, they observed that “the infection of a node enables the 911.re user to access shared resources on the network such as local intranet portals or other services.”

“It also enables the end user to probe the LAN network of the infected node,” the paper continues. “Using the internal router, it would be possible to poison the DNS cache of the LAN router of the infected node, enabling further attacks.”

THE INTERNET NEVER FORGETS

A review of the clues left behind by 911’s early days on the Internet paint a more complete picture of this long-running proxy network. The domain names used by 911 over the years have a few common elements in their original WHOIS registration records, including the address ustraffic@qq.com and a Yunhe Wang from Beijing.

That ustraffic email is tied to a small number of interesting domains, including browsingguard[.]com, cleantraffic[.]net, execlean[.]net, proxygate[.]net, and flashupdate[.]net.

A cached copy of flashupdate[.]net available at the Wayback Machine shows that in 2016 this domain was used for the “ExE Bucks” affiliate program, a pay-per-install business which catered to people already running large collections of hacked computers or compromised websites. Affiliates were paid a set amount for each installation of the software, with higher commissions for installs in more desirable nations, particularly Europe, Canada and the United States.

“We load only one software — it’s a Socks5 proxy program,” read the message to ExE Bucks affiliates. The website said affiliates were free to spread the proxy software by any means available (i.e. “all promotion methods allowed”). The website’s copyright suggests the ExE Bucks affiliate program dates back to 2012.

Another domain tied to the ustraffic@qq.com email in 2016 was ExeClean[.]net, a service that advertised to cybercriminals seeking to obfuscate their malicious software so that it goes undetected by all or at least most of the major antivirus products on the market.

“Our technology ensures the maximum security from reverse engineering and antivirus detections,” ExEClean promised.

Yet another domain connected to the ustraffic email is p2pshare[.]net, which advertised “free unlimited internet file-sharing platform” for those who agreed to install their software.

Still more domains associated with ustraffic@qq.com suggest 911’s proxy has been disguised as security updates for video player plugins, including flashplayerupdate[.]xyz, mediaplayerupdate[.]xyz, and videoplayerupdate[.]xyz.

The earliest version of the 911 website available from the Wayback Machine is from 2016. A sister service called proxygate[.]net launched roughly a year prior to 911 as a “free” public test of the budding new residential proxy service. “Basically using clients to route for everyone,” was how Proxygate described itself in 2016.

For more than a year after its founding, the 911 website was written entirely in Simplified Chinese. The service has only ever accepted payment via virtual currencies such as Bitcoin and Monero, as well as Alipay and China UnionPay, both payment platforms based in China.

Initially, the terms and conditions of 911’s “End User License Agreement (EULA) named a company called Wugaa Enterprises LLC, which was registered in California in 2016. Records from the California Secretary of State office show that in November 2016, Wugaa Enterprises said it was in the Internet advertising business, and had named as its CEO as one Nicolae Aurelian Mazgarean of Brasov, Romania.

A search of European VAT numbers shows the same Brasov, RO address tied to an enterprise called PPC Leads SRL (in the context of affiliate-based marketing, “PPC” generally refers to the term “pay-per-click”).

911’s EULA would later change its company name and address in 2017, to International Media Ltd. in the British Virgin Islands. That is the same information currently displayed on the 911 website.

The EULA attached to 911 software downloaded from browsingguard[.]com (tied to the same ustraffic@qq email that registered 911) references a company called Gold Click Limited. According to the UK Companies House, Gold Click Limited was registered in 2016 to a 34-year-old Yunhe Wang from Beijing City. Many of the WHOIS records for the above mentioned domains also include the name Yunhe Wang, or some variation thereof.

In a response to questions from KrebsOnSecurity, 911 said the researchers were wrong, and that 911 has nothing to do with any of the other domains mentioned above.

“We have 911 SDK link and how it works described clearly in the “Terms of use” of affiliated partners products, and we have details of how the community powered network works on our webpages,” read an email response.

“Besides that, for protecting the end users, we banned many domains’ access and blocked the vulnerable ports, e.g. spamming emails, and torrent is not possible from the 911 network,” the reply continued. “Same as scanning and many others…Accessing to the Lan network and router is also blocked. We are monitoring 911 user’s account closely, once any abnormal behavior detected, we suspend the user’s account right away.”

FORUM ACTIVITY?

911 has remained one of the most popular services among denizens of the cybercrime underground for years, becoming almost shorthand for connecting to that “last mile” of cybercrime. Namely, the ability to route one’s malicious traffic through a computer that is geographically close to the consumer whose credit card they’re about to charge at some website, or whose bank account they’re about to empty.

Given the frequency with which 911 has been praised by cybercrooks on the top forums, it was odd to find the proprietors of 911 do not appear to have created any official support account for the service on any of several dozen forums reviewed by this author going back a decade. However there are two cybercriminal identities on the forums that have responded to individual 911 help requests, and who promoted the sale of 911 accounts via their handles.

Both of these identities were active on the crime forum fl.l33t[.]su between 2016 and 2019. The user “Transfer” advertised and sold access to 911 from 2016 to 2018, amid many sales threads where they advertised expensive electronics and other consumer goods that were bought online with stolen credit cards.

In a 2017 discussion on fl.l33t[.]su, the user who picked the handle “527865713” could be seen answering private messages in response to help inquiries seeking someone at 911. That identity is tied to an individual who for years advertised the ability to receive and relay large wire transfers from China.

One ad from this user in 2016 offered a “China wire service” focusing on Western Union payments, where “all transfers are accepted in China.” The service charged 20 percent of all “scam wires,” unauthorized wire transfers resulting from bank account takeovers or scams like CEO impersonation schemes.

911 TODAY

In August 2021, 911’s biggest competitor — a 15-year-old proxy network built on malware-compromised PCs called VIP72 — abruptly closed up shop. Almost overnight, an overwhelming number of former VIP72 customers began shifting their proxy activities to 911.

That’s according to Riley Kilmer, co-founder of Spur.us — a security company that monitors anonymity services. Kilmer said 911 also gained an influx of new customers after the Jan. 2022 closure of LuxSocks, another malware-based proxy network.

“911’s user base skyrocketed after VIP72 and then LuxSocks went away,” Kilmer said. “And it’s not hard to see why. 911 and VIP72 are both Windows-based apps that operate in a similar way, where you buy private access to IPs.”

Kilmer said 911 is interesting because it appears to be based in China, while nearly all of the other major proxy networks are Russian-backed or Russian-based.

“They have two basic methods to get new IPs,” Kilmer said. “The free VPN apps, and the other is trojanized torrents. They’ll re-upload Photoshop and stuff like that so that it’s backdoored with the 911 proxy. They claim the proxy is bundled with legitimate software and that users all agree to their Terms of Service, meanwhile they can hide behind the claim that it was some affiliate who installed the software, not them.”

Kilmer said at last count, 911 had nearly 200,000 proxy nodes for sale, spanning more than 200 countries: The largest geographic concentration is the United States, where more than 42,000 proxies are currently for rent by the service.

PARTING THOUGHTS

Beware of “free” or super low-cost VPN services. Proper VPN services are not cheap to operate, so the revenue for the service has to come from somewhere. And there are countless “free” VPN services that are anything but, as we’ve seen with 911.

In general, the rule of thumb for transacting online is that if you’re not the paying customer, then you and/or your devices are probably the product that’s being sold to others. Many free VPN services will enlist users as VPN nodes for others to use, and some even offset costs by collecting and reselling data from their users.

All VPN providers claim to prioritize the privacy of their users, but many then go on to collect and store all manner of personal and financial data from those customers. Others are fairly opaque about their data collection and retention policies.

I’ve largely avoided wading into the fray about which VPN services are best, but there are so many shady and just plain bad ones out there that I’d be remiss if I didn’t mention one VPN provider whose business practices and transparency of operation consistently distinguish them from the rest. If maintaining your privacy and anonymity are primary concerns for you as a VPN user, check out Mullvad.net.

Let me make clear that KrebsOnSecurity does not have any financial or business ties to this company (for the avoidance of doubt, this post doesn’t even link to them). I mention it only because I’ve long been impressed with their candor and openness, and because Mullvad goes out of its way to discourage customers from sharing personal or financial data.

To that end, Mullvad will even accept mailed payments of cash to fund accounts, quite a rarity these days. More importantly, the service doesn’t ask users to share phone numbers, email addresses or any other personal information. Nor does it require customers to create passwords: Each subscription can be activated just by entering a Mullvad account number (woe to those who lose their account number).

I wish more companies would observe this remarkably economical security practice, which boils down to the mantra, “You don’t have to protect what you don’t collect.”

Update, July 24, 11:15 a.m. ET: 911’s homepage now includes a banner saying the service has halted new registrations and payments. “We are reviewing our network and adding a series of security measures to prevent misuse of our services,” the message reads. “Proxy balance top-up and new user registration are closed. We are reviewing every existing user, to ensure their usage is legit and [in] compliance with our Terms of Service.”

Update, July 30, 10:07 a.m. ET: 911 announced on July 28 that it is permanently closing down, following a series of data breaches this month that 911 says resulted in the deletion of customer data.