Virtual private networking (VPN) companies market their services as a way to prevent anyone from snooping on your Internet usage. But new research suggests this is a dangerous assumption when connecting to a VPN via an untrusted network, because attackers on the same network could force a target’s traffic off of the protection provided by their VPN without triggering any alerts to the user.
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When a device initially tries to connect to a network, it broadcasts a message to the entire local network stating that it is requesting an Internet address. Normally, the only system on the network that notices this request and replies is the router responsible for managing the network to which the user is trying to connect.
The machine on a network responsible for fielding these requests is called a Dynamic Host Configuration Protocol (DHCP) server, which will issue time-based leases for IP addresses. The DHCP server also takes care of setting a specific local address — known as an Internet gateway — that all connecting systems will use as a primary route to the Web.
VPNs work by creating a virtual network interface that serves as an encrypted tunnel for communications. But researchers at Leviathan Security say they’ve discovered it’s possible to abuse an obscure feature built into the DHCP standard so that other users on the local network are forced to connect to a rogue DHCP server.
“Our technique is to run a DHCP server on the same network as a targeted VPN user and to also set our DHCP configuration to use itself as a gateway,” Leviathan researchers Lizzie Moratti and Dani Cronce wrote. “When the traffic hits our gateway, we use traffic forwarding rules on the DHCP server to pass traffic through to a legitimate gateway while we snoop on it.”
The feature being abused here is known as DHCP option 121, and it allows a DHCP server to set a route on the VPN user’s system that is more specific than those used by most VPNs. Abusing this option, Leviathan found, effectively gives an attacker on the local network the ability to set up routing rules that have a higher priority than the routes for the virtual network interface that the target’s VPN creates.
“Pushing a route also means that the network traffic will be sent over the same interface as the DHCP server instead of the virtual network interface,” the Leviathan researchers said. “This is intended functionality that isn’t clearly stated in the RFC [standard]. Therefore, for the routes we push, it is never encrypted by the VPN’s virtual interface but instead transmitted by the network interface that is talking to the DHCP server. As an attacker, we can select which IP addresses go over the tunnel and which addresses go over the network interface talking to our DHCP server.”
Leviathan found they could force VPNs on the local network that already had a connection to arbitrarily request a new one. In this well-documented tactic, known as a DHCP starvation attack, an attacker floods the DHCP server with requests that consume all available IP addresses that can be allocated. Once the network’s legitimate DHCP server is completely tied up, the attacker can then have their rogue DHCP server respond to all pending requests.
“This technique can also be used against an already established VPN connection once the VPN user’s host needs to renew a lease from our DHCP server,” the researchers wrote. “We can artificially create that scenario by setting a short lease time in the DHCP lease, so the user updates their routing table more frequently. In addition, the VPN control channel is still intact because it already uses the physical interface for its communication. In our testing, the VPN always continued to report as connected, and the kill switch was never engaged to drop our VPN connection.”
The researchers say their methods could be used by an attacker who compromises a DHCP server or wireless access point, or by a rogue network administrator who owns the infrastructure themselves and maliciously configures it. Alternatively, an attacker could set up an “evil twin” wireless hotspot that mimics the signal broadcast by a legitimate provider.
Bill Woodcock is executive director at Packet Clearing House, a nonprofit based in San Francisco. Woodcock said Option 121 has been included in the DHCP standard since 2002, which means the attack described by Leviathan has technically been possible for the last 22 years.
“They’re realizing now that this can be used to circumvent a VPN in a way that’s really problematic, and they’re right,” Woodcock said.
Woodcock said anyone who might be a target of spear phishing attacks should be very concerned about using VPNs on an untrusted network.
“Anyone who is in a position of authority or maybe even someone who is just a high net worth individual, those are all very reasonable targets of this attack,” he said. “If I were trying to do an attack against someone at a relatively high security company and I knew where they typically get their coffee or sandwich at twice a week, this is a very effective tool in that toolbox. I’d be a little surprised if it wasn’t already being exploited in that way, because again this isn’t rocket science. It’s just thinking a little outside the box.”
Successfully executing this attack on a network likely would not allow an attacker to see all of a target’s traffic or browsing activity. That’s because for the vast majority of the websites visited by the target, the content is encrypted (the site’s address begins with https://). However, an attacker would still be able to see the metadata — such as the source and destination addresses — of any traffic flowing by.
KrebsOnSecurity shared Leviathan’s research with John Kristoff, founder of dataplane.org and a PhD candidate in computer science at the University of Illinois Chicago. Kristoff said practically all user-edge network gear, including WiFi deployments, support some form of rogue DHCP server detection and mitigation, but that it’s unclear how widely deployed those protections are in real-world environments.
“However, and I think this is a key point to emphasize, an untrusted network is an untrusted network, which is why you’re usually employing the VPN in the first place,” Kristoff said. “If [the] local network is inherently hostile and has no qualms about operating a rogue DHCP server, then this is a sneaky technique that could be used to de-cloak some traffic – and if done carefully, I’m sure a user might never notice.”
According to Leviathan, there are several ways to minimize the threat from rogue DHCP servers on an unsecured network. One is using a device powered by the Android operating system, which apparently ignores DHCP option 121.
Relying on a temporary wireless hotspot controlled by a cellular device you own also effectively blocks this attack.
“They create a password-locked LAN with automatic network address translation,” the researchers wrote of cellular hot-spots. “Because this network is completely controlled by the cellular device and requires a password, an attacker should not have local network access.”
Leviathan’s Moratti said another mitigation is to run your VPN from inside of a virtual machine (VM) — like Parallels, VMware or VirtualBox. VPNs run inside of a VM are not vulnerable to this attack, Moratti said, provided they are not run in “bridged mode,” which causes the VM to replicate another node on the network.
In addition, a technology called “deep packet inspection” can be used to deny all in- and outbound traffic from the physical interface except for the DHCP and the VPN server. However, Leviathan says this approach opens up a potential “side channel” attack that could be used to determine the destination of traffic.
“This could be theoretically done by performing traffic analysis on the volume a target user sends when the attacker’s routes are installed compared to the baseline,” they wrote. “In addition, this selective denial-of-service is unique as it could be used to censor specific resources that an attacker doesn’t want a target user to connect to even while they are using the VPN.”
Moratti said Leviathan’s research shows that many VPN providers are currently making promises to their customers that their technology can’t keep.
“VPNs weren’t designed to keep you more secure on your local network, but to keep your traffic more secure on the Internet,” Moratti said. “When you start making assurances that your product protects people from seeing your traffic, there’s an assurance or promise that can’t be met.”
A copy of Leviathan’s research, along with code intended to allow others to duplicate their findings in a lab environment, is available here.
The head of counterintelligence for a division of the Russian Federal Security Service (FSB) was sentenced last week to nine years in a penal colony for accepting a USD $1.7 million bribe to ignore the activities of a prolific Russian cybercrime group that hacked thousands of e-commerce websites. The protection scheme was exposed in 2022 when Russian authorities arrested six members of the group, which sold millions of stolen payment cards at flashy online shops like Trump’s Dumps.
A now-defunct carding shop that sold stolen credit cards and invoked 45’s likeness and name.
As reported by The Record, a Russian court last week sentenced former FSB officer Grigory Tsaregorodtsev for taking a $1.7 million bribe from a cybercriminal group that was seeking a “roof,” a well-placed, corrupt law enforcement official who could be counted on to both disregard their illegal hacking activities and run interference with authorities in the event of their arrest.
Tsaregorodtsev was head of the counterintelligence department for a division of the FSB based in Perm, Russia. In February 2022, Russian authorities arrested six men in the Perm region accused of selling stolen payment card data. They also seized multiple carding shops run by the gang, including Ferum Shop, Sky-Fraud, and Trump’s Dumps, a popular fraud store that invoked the 45th president’s likeness and promised to “make credit card fraud great again.”
All of the domains seized in that raid were registered by an IT consulting company in Perm called Get-net LLC, which was owned in part by Artem Zaitsev — one of the six men arrested. Zaitsev reportedly was a well-known programmer whose company supplied services and leasing to the local FSB field office.
The message for Trump’s Dumps users left behind by Russian authorities that seized the domain in 2022.
Russian news sites report that Internal Affairs officials with the FSB grew suspicious when Tsaregorodtsev became a little too interested in the case following the hacking group’s arrests. The former FSB agent had reportedly assured the hackers he could have their case transferred and that they would soon be free.
But when that promised freedom didn’t materialize, four the of the defendants pulled the walls down on the scheme and brought down their own roof. The FSB arrested Tsaregorodtsev, and seized $154,000 in cash, 100 gold bars, real estate and expensive cars.
At Tsaregorodtsev’s trial, his lawyers argued that their client wasn’t guilty of bribery per se, but that he did admit to fraud because he was ultimately unable to fully perform the services for which he’d been hired.
The Russian news outlet Kommersant reports that all four of those who cooperated were released with probation or correctional labor. Zaitsev received a sentence of 3.5 years in prison, and defendant Alexander Kovalev got four years.
In 2017, KrebsOnSecurity profiled Trump’s Dumps, and found the contact address listed on the site was tied to an email address used to register more than a dozen domains that were made to look like legitimate Javascript calls many e-commerce sites routinely make to process transactions — such as “js-link[dot]su,” “js-stat[dot]su,” and “js-mod[dot]su.”
Searching on those malicious domains revealed a 2016 report from RiskIQ, which shows the domains featured prominently in a series of hacking campaigns against e-commerce websites. According to RiskIQ, the attacks targeted online stores running outdated and unpatched versions of shopping cart software from Magento, Powerfront and OpenCart.
Those shopping cart flaws allowed the crooks to install “web skimmers,” malicious Javascript used to steal credit card details and other information from payment forms on the checkout pages of vulnerable e-commerce sites. The stolen customer payment card details were then sold on sites like Trump’s Dumps and Sky-Fraud.
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The U.S. government is warning that “smart locks” securing entry to an estimated 50,000 dwellings nationwide contain hard-coded credentials that can be used to remotely open any of the locks. The lock’s maker Chirp Systems remains unresponsive, even though it was first notified about the critical weakness in March 2021. Meanwhile, Chirp’s parent company, RealPage, Inc., is being sued by multiple U.S. states for allegedly colluding with landlords to illegally raise rents.
On March 7, 2024, the U.S. Cybersecurity & Infrastructure Security Agency (CISA) warned about a remotely exploitable vulnerability with “low attack complexity” in Chirp Systems smart locks.
“Chirp Access improperly stores credentials within its source code, potentially exposing sensitive information to unauthorized access,” CISA’s alert warned, assigning the bug a CVSS (badness) rating of 9.1 (out of a possible 10). “Chirp Systems has not responded to requests to work with CISA to mitigate this vulnerability.”
Matt Brown, the researcher CISA credits with reporting the flaw, is a senior systems development engineer at Amazon Web Services. Brown said he discovered the weakness and reported it to Chirp in March 2021, after the company that manages his apartment building started using Chirp smart locks and told everyone to install Chirp’s app to get in and out of their apartments.
“I use Android, which has a pretty simple workflow for downloading and decompiling the APK apps,” Brown told KrebsOnSecurity. “Given that I am pretty picky about what I trust on my devices, I downloaded Chirp and after decompiling, found that they were storing passwords and private key strings in a file.”
Using those hard-coded credentials, Brown found an attacker could then connect to an application programming interface (API) that Chirp uses which is managed by smart lock vendor August.com, and use that to enumerate and remotely lock or unlock any door in any building that uses the technology.
Update, April 18, 11:55 a.m. ET: August has provided a statement saying it does not believe August or Yale locks are vulnerable to the hack described by Brown.
“We were recently made aware of a vulnerability disclosure regarding access control systems provided by Chirp, using August and Yale locks in multifamily housing,” the company said. “Upon learning of these reports, we immediately and thoroughly investigated these claims. Our investigation found no evidence that would substantiate the vulnerability claims in either our product or Chirp’s as it relates to our systems.”
Update, April 25, 2:45 p.m. ET: Based on feedback from Chirp, CISA has downgraded the severity of this flaw and revised their security advisory to say that the hard-coded credentials do not appear to expose the devices to remote locking or unlocking. CISA says the hardcoded credentials could be used by an attacker within the range of Bluetooth (~30 meters) “to change the configuration settings within the Bluetooth beacon, effectively removing Bluetooth visibility from the device. This does not affect the device’s ability to lock or unlock access points, and access points can still be operated remotely by unauthorized users via other means.”
Brown said when he complained to his leasing office, they sold him a small $50 key fob that uses Near-Field Communications (NFC) to toggle the lock when he brings the fob close to his front door. But he said the fob doesn’t eliminate the ability for anyone to remotely unlock his front door using the exposed credentials and the Chirp mobile app.
Also, the fobs pass the credentials to his front door over the air in plain text, meaning someone could clone the fob just by bumping against him with a smartphone app made to read and write NFC tags.
Neither August nor Chirp Systems responded to requests for comment. It’s unclear exactly how many apartments and other residences are using the vulnerable Chirp locks, but multiple articles about the company from 2020 state that approximately 50,000 units use Chirp smart locks with August’s API.
Roughly a year before Brown reported the flaw to Chirp Systems, the company was bought by RealPage, a firm founded in 1998 as a developer of multifamily property management and data analytics software. In 2021, RealPage was acquired by the private equity giant Thoma Bravo.
Brown said the exposure he found in Chirp’s products is “an obvious flaw that is super easy to fix.”
“It’s just a matter of them being motivated to do it,” he said. “But they’re part of a private equity company now, so they’re not answerable to anybody. It’s too bad, because it’s not like residents of [the affected] properties have another choice. It’s either agree to use the app or move.”
In October 2022, an investigation by ProPublica examined RealPage’s dominance in the rent-setting software market, and that it found “uses a mysterious algorithm to help landlords push the highest possible rents on tenants.”
“For tenants, the system upends the practice of negotiating with apartment building staff,” ProPublica found. “RealPage discourages bargaining with renters and has even recommended that landlords in some cases accept a lower occupancy rate in order to raise rents and make more money. One of the algorithm’s developers told ProPublica that leasing agents had ‘too much empathy’ compared to computer generated pricing.”
Last year, the U.S. Department of Justice threw its weight behind a massive lawsuit filed by dozens of tenants who are accusing the $9 billion apartment software company of helping landlords collude to inflate rents.
In February 2024, attorneys general for Arizona and the District of Columbia sued RealPage, alleging RealPage’s software helped create a rental monopoly.
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