Calendar Meeting Links Used to Spread Mac Malware

Malicious hackers are targeting people in the cryptocurrency space in attacks that start with a link added to the target’s calendar at Calendly, a popular application for scheduling appointments and meetings. The attackers impersonate established cryptocurrency investors and ask to schedule a video conference call. But clicking the meeting link provided by the scammers prompts the user to run a script that quietly installs malware on macOS systems.

KrebsOnSecurity recently heard from a reader who works at a startup that is seeking investment for building a new blockchain platform for the Web. The reader spoke on condition that their name not be used in this story, so for the sake of simplicity we’ll call him Doug.

Being in the cryptocurrency scene, Doug is also active on the instant messenger platform Telegram. Earlier this month, Doug was approached by someone on Telegram whose profile name, image and description said they were Ian Lee, from Signum Capital, a well-established investment firm based in Singapore. The profile also linked to Mr. Lee’s Twitter/X account, which features the same profile image.

The investor expressed interest in financially supporting Doug’s startup, and asked if Doug could find time for a video call to discuss investment prospects. Sure, Doug said, here’s my Calendly profile, book a time and we’ll do it then.

When the day and time of the scheduled meeting with Mr. Lee arrived, Doug clicked the meeting link in his calendar but nothing happened. Doug then messaged the Mr. Lee account on Telegram, who said there was some kind of technology issue with the video platform, and that their IT people suggested using a different meeting link.

Doug clicked the new link, but instead of opening up a videoconference app, a message appeared on his Mac saying the video service was experiencing technical difficulties.

“Some of our users are facing issues with our service,” the message read. “We are actively working on fixing these problems. Please refer to this script as a temporary solution.”

Doug said he ran the script, but nothing appeared to happen after that, and the videoconference application still wouldn’t start. Mr. Lee apologized for the inconvenience and said they would have to reschedule their meeting, but he never responded to any of Doug’s follow-up messages.

It didn’t dawn on Doug until days later that the missed meeting with Mr. Lee might have been a malware attack. Going back to his Telegram client to revisit the conversation, Doug discovered his potential investor had deleted the meeting link and other bits of conversation from their shared chat history.

In a post to its Twitter/X account last month, Signum Capital warned that a fake profile pretending to be their employee Mr. Lee was trying to scam people on Telegram.

The file that Doug ran is a simple Apple Script (file extension “.scpt”) that downloads and executes a malicious trojan made to run on macOS systems. Unfortunately for us, Doug freaked out after deciding he’d been tricked — backing up his important documents, changing his passwords, and then reinstalling macOS on his computer. While this a perfectly sane response, it means we don’t have the actual malware that was pushed to his Mac by the script.

But Doug does still have a copy of the malicious script that was downloaded from clicking the meeting link (the online host serving that link is now offline). A search in Google for a string of text from that script turns up a December 2023 blog post from cryptocurrency security firm SlowMist about phishing attacks on Telegram from North Korean state-sponsored hackers.

“When the project team clicks the link, they encounter a region access restriction,” SlowMist wrote. “At this point, the North Korean hackers coax the team into downloading and running a ‘location-modifying’ malicious script. Once the project team complies, their computer comes under the control of the hackers, leading to the theft of funds.”

SlowMist says the North Korean phishing scams used the “Add Custom Link” feature of the Calendly meeting scheduling system on event pages to insert malicious links and initiate phishing attacks.

“Since Calendly integrates well with the daily work routines of most project teams, these malicious links do not easily raise suspicion,” the blog post explains. “Consequently, the project teams may inadvertently click on these malicious links, download, and execute malicious code.”

SlowMist said the malware downloaded by the malicious link in their case comes from a North Korean hacking group dubbed “BlueNoroff, which Kaspersky Labs says is a subgroup of the Lazarus hacking group.

“A financially motivated threat actor closely connected with Lazarus that targets banks, casinos, fin-tech companies, POST software and cryptocurrency businesses, and ATMs,” Kaspersky wrote of BlueNoroff in Dec. 2023.

The North Korean regime is known to use stolen cryptocurrencies to fund its military and other state projects. A recent report from Recorded Future finds the Lazarus Group has stolen approximately $3 billion in cryptocurrency over the past six years.

While there is still far more malware out there today targeting Microsoft Windows PCs, the prevalence of information-stealing trojans aimed at macOS users is growing at a steady clip. MacOS computers include X-Protect, Apple’s built-in antivirus technology. But experts say attackers are constantly changing the appearance and behavior of their malware to evade X-Protect.

“Recent updates to macOS’s XProtect signature database indicate that Apple are aware of the problem, but early 2024 has already seen a number of stealer families evade known signatures,” security firm SentinelOne wrote in January.

According to Chris Ueland from the threat hunting platform Hunt.io, the Internet address of the fake meeting website Doug was tricked into visiting (104.168.163,149) hosts or very recently hosted about 75 different domain names, many of which invoke words associated with videoconferencing or cryptocurrency. Those domains indicate this North Korean hacking group is hiding behind a number of phony crypto firms, like the six-month-old website for Cryptowave Capital (cryptowave[.]capital).

In a statement shared with KrebsOnSecurity, Calendly said it was aware of these types of social engineering attacks by cryptocurrency hackers.

“To help prevent these kinds of attacks, our security team and partners have implemented a service to automatically detect fraud and impersonations that could lead to social engineering,” the company said. “We are also actively scanning content for all our customers to catch these types of malicious links and to prevent hackers earlier on. Additionally, we intend to add an interstitial page warning users before they’re redirected away from Calendly to other websites. Along with the steps we’ve taken, we recommend users stay vigilant by keeping their software secure with running the latest updates and verifying suspicious links through tools like VirusTotal to alert them of possible malware. We are continuously strengthening the cybersecurity of our platform to protect our customers.”

The increasing frequency of new Mac malware is a good reminder that Mac users should not depend on security software and tools to flag malicious files, which are frequently bundled with or disguised as legitimate software.

As KrebsOnSecurity has advised Windows users for years, a good rule of safety to live by is this: If you didn’t go looking for it, don’t install it. Following this mantra heads off a great deal of malware attacks, regardless of the platform used. When you do decide to install a piece of software, make sure you are downloading it from the original source, and then keep it updated with any new security fixes.

On that last front, I’ve found it’s a good idea not to wait until the last minute to configure my system before joining a scheduled videoconference call. Even if the call uses software that is already on my computer, it is often the case that software updates are required before the program can be used, and I’m one of those weird people who likes to review any changes to the software maker’s privacy policies or user agreements before choosing to install updates.

Most of all, verify new contacts from strangers before accepting anything from them. In this case, had Doug simply messaged Mr. Lee’s real account on Twitter/X or contacted Signum Capital directly, he would discovered that the real Mr. Lee never asked for a meeting.

If you’re approached in a similar scheme, the response from the would-be victim documented in the SlowMist blog post is probably the best.

Update: Added comment from Calendly.

Russia Sends Cybersecurity CEO to Jail for 14 Years

The Russian government today handed down a treason conviction and 14-year prison sentence on Iyla Sachkov, the former founder and CEO of one of Russia’s largest cybersecurity firms. Sachkov, 37, has been detained for nearly two years under charges that the Kremlin has kept classified and hidden from public view, and he joins a growing roster of former Russian cybercrime fighters who are now serving hard time for farcical treason convictions.

In 2003, Sachkov founded Group-IB, a cybersecurity and digital forensics company that quickly earned a reputation for exposing and disrupting large-scale cybercrime operations, including quite a few that were based in Russia and stealing from Russian companies and citizens.

In September 2021, the Kremlin issued treason charges against Sachkov, although it has refused to disclose any details about the allegations. Sachkov pleaded not guilty. After a three-week “trial” that was closed to the public, Sachkov was convicted of treason and sentenced to 14 years in prison. Prosecutors had asked for 18 years.

Group-IB relocated its headquarters to Singapore several years ago, although it did not fully exit the Russian market until April 2023. In a statement, Group-IB said that during their founder’s detainment, he was denied the right to communicate — no calls, no letters — with the outside world for the first few months, and was deprived of any visits from family and friends.

“Ultimately, Ilya has been denied a chance for an impartial trial,” reads a blog post on the company’s site. “All the materials of the case are kept classified, and all hearings were held in complete secrecy with no public scrutiny. As a result, we might never know the pretext for his conviction.”

Prior to his arrest in 2021, Sachkov publicly chastised the Kremlin for turning a blind eye to the epidemic of ransomware attacks coming from Russia. In a speech covered by the Financial Times in 2021, Sachkov railed against the likes of Russian hacker Maksim Yakubets, the accused head of a hacking group called Evil Corp. that U.S. officials say has stolen hundreds of millions of dollars over the past decade.

“Yakubets has been spotted driving around Moscow in a fluorescent camouflage Lamborghini, with a custom licence plate that reads ‘THIEF,'” FT’s Max Seddon wrote. “He also ‘provides direct assistance to the Russian government’s malicious cyber efforts,’ according to US Treasury sanctions against him.”

In December 2021, Bloomberg reported that Sachkov was alleged to have given the United States information about the Russian “Fancy Bear” operation that sought to influence the 2016 U.S. election. Fancy Bear is one of several names (e.g., APT28) for an advanced Russian cyber espionage group that has been linked to the Russian military intelligence agency GRU.

In 2019, a Moscow court meted out a 22-year prison sentence for alleged treason charges against Sergei Mikhailov, formerly deputy chief of Russia’s top anti-cybercrime unit. The court also levied a 14-year sentence against Ruslan Stoyanov, a senior employee at Kaspersky Lab. Both men maintained their innocence throughout the trial, and the supposed reason for the treason charges has never been disclosed.

Following their dramatic arrests in 2016, some media outlets reported that the men were suspected of having tipped off American intelligence officials about those responsible for Russian hacking activities tied to the 2016 U.S. presidential election.

That’s because two others arrested for treason at the same time — Mikhailov subordinates Georgi Fomchenkov and Dmitry Dokuchaev — were reported by Russian media to have helped the FBI investigate Russian servers linked to the 2016 hacking of the Democratic National Committee.

3CX Breach Was a Double Supply Chain Compromise

We learned some remarkable new details this week about the recent supply-chain attack on VoIP software provider 3CX. The lengthy, complex intrusion has all the makings of a cyberpunk spy novel: North Korean hackers using legions of fake executive accounts on LinkedIn to lure people into opening malware disguised as a job offer; malware targeting Mac and Linux users working at defense and cryptocurrency firms; and software supply-chain attacks nested within earlier supply chain attacks.

In late March 2023, 3CX disclosed that its desktop applications for both Windows and macOS were compromised with malicious code that gave attackers the ability to download and run code on all machines where the app was installed. 3CX says it has more than 600,000 customers and 12 million users in a broad range of industries, including aerospace, healthcare and hospitality.

3CX hired incident response firm Mandiant, which released a report on Wednesday that said the compromise began in 2022 when a 3CX employee installed a malware-laced software package distributed via an earlier software supply chain compromise that began with a tampered installer for X_TRADER, a software package provided by Trading Technologies.

“This is the first time Mandiant has seen a software supply chain attack lead to another software supply chain attack,” reads the April 20 Mandiant report.

Mandiant found the earliest evidence of compromise uncovered within 3CX’s network was through the VPN using the employee’s corporate credentials, two days after the employee’s personal computer was compromised.

“Eventually, the threat actor was able to compromise both the Windows and macOS build environments,” 3CX said in an April 20 update on their blog.

Mandiant concluded that the 3CX attack was orchestrated by the North Korean state-sponsored hacking group known as Lazarus, a determination that was independently reached earlier by researchers at Kaspersky Lab and Elastic Security.

Mandiant found the compromised 3CX software would download malware that sought out new instructions by consulting encrypted icon files hosted on GitHub. The decrypted icon files revealed the location of the malware’s control server, which was then queried for a third stage of the malware compromise — a password stealing program dubbed ICONICSTEALER.

Meanwhile, the security firm ESET today published research showing remarkable similarities between the malware used in the 3CX supply chain attack and Linux-based malware that was recently deployed via fake job offers from phony executive profiles on LinkedIn. The researchers said this was the first time Lazarus had been spotted deploying malware aimed at Linux users.

As reported in a series last summer here, LinkedIn has been inundated this past year by fake executive profiles for people supposedly employed at a range of technology, defense, energy and financial companies. In many cases, the phony profiles spoofed chief information security officers at major corporations, and some attracted quite a few connections before their accounts were terminated.

Mandiant, Proofpoint and other experts say Lazarus has long used these bogus LinkedIn profiles to lure targets into opening a malware-laced document that is often disguised as a job offer. This ongoing North Korean espionage campaign using LinkedIn was first documented in August 2020 by ClearSky Security, which said the Lazarus group operates dozens of researchers and intelligence personnel to maintain the campaign globally.

Microsoft Corp., which owns LinkedIn, said in September 2022 that it had detected a wide range of social engineering campaigns using a proliferation of phony LinkedIn accounts. Microsoft said the accounts were used to impersonate recruiters at technology, defense and media companies, and to entice people into opening a malicious file. Microsoft found the attackers often disguised their malware as legitimate open-source software like Sumatra PDF and the SSH client Putty.

Microsoft attributed those attacks to North Korea’s Lazarus hacking group, although they’ve traditionally referred to this group as “ZINC“. That is, until earlier this month, when Redmond completely revamped the way it names threat groups; Microsoft now references ZINC as “Diamond Sleet.”

The ESET researchers said they found a new fake job lure tied to an ongoing Lazarus campaign on LinkedIn designed to compromise Linux operating systems. The malware was found inside of a document that offered an employment contract at the multinational bank HSBC.

“A few weeks ago, a native Linux payload was found on VirusTotal with an HSBC-themed PDF lure,” wrote ESET researchers Peter Kalnai and Marc-Etienne M.Leveille. “This completes Lazarus’s ability to target all major desktop operating systems. In this case, we were able to reconstruct the full chain, from the ZIP file that delivers a fake HSBC job offer as a decoy, up until the final payload.”

ESET said the malicious PDF file used in the scheme appeared to have a file extension of “.pdf,” but that this was a ruse. ESET discovered that the dot in the filename wasn’t a normal period but instead a Unicode character (U+2024) representing a “leader dot,” which is often used in tables of contents to connect section headings with the page numbers on which those sections begin.

“The use of the leader dot in the filename was probably an attempt to trick the file manager into treating the file as an executable instead of a PDF,” the researchers continued. “This could cause the file to run when double-clicked instead of opening it with a PDF viewer.”

ESET said anyone who opened the file would see a decoy PDF with a job offer from HSBC, but in the background the executable file would download additional malware payloads. The ESET team also found the malware was able to manipulate the program icon displayed by the malicious PDF, possibly because fiddling with the file extension could cause the user’s system to display a blank icon for the malware lure.

Kim Zetter, a veteran Wired.com reporter and now independent security journalist, interviewed Mandiant researchers who said they expect “many more victims” will be discovered among the customers of Trading Technologies and 3CX now that news of the compromised software programs is public.

“Mandiant informed Trading Technologies on April 11 that its X_Trader software had been compromised, but the software maker says it has not had time to investigate and verify Mandiant’s assertions,” Zetter wrote in her Zero Day newsletter on Substack. For now, it remains unclear whether the compromised X_Trader software was downloaded by people at other software firms.

If there’s a silver lining here, the X_Trader software had been decommissioned in April 2020 — two years before the hackers allegedly embedded malware in it.

“The company hadn’t released new versions of the software since that time and had stopped providing support for the product, making it a less-than-ideal vector for the North Korean hackers to infect customers,” Zetter wrote.