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Thousands of Linux systems infected by stealthy malware since 2021 [arstechnica.com]:

Thousands of machines running Linux have been infected by a malware strain that’s notable for its stealth, the number of misconfigurations it can exploit, and the breadth of malicious activities it can perform, researchers reported Thursday.

The malware has been circulating since at least 2021. It gets installed by exploiting more than 20,000 common misconfigurations, a capability that may make millions of machines connected to the Internet potential targets, researchers from Aqua Security said. It can also exploit CVE-2023-33426, a vulnerability with a severity rating of 10 out of 10 that was patched last year in Apache RocketMQ, a messaging and streaming platform that’s found on many Linux machines.

Perfctl storm

The researchers are calling the malware Perfctl, the name of a malicious component that surreptitiously mines cryptocurrency. The unknown developers of the malware gave the process a name that combines the perf Linux monitoring tool and ctl, an abbreviation commonly used with command line tools. A signature characteristic of Perfctl is its use of process and file names that are identical or similar to those commonly found in Linux environments. The naming convention is one of the many ways the malware attempts to escape notice of infected users.

Perfctl further cloaks itself using a host of other tricks. One is that it installs many of its components as rootkits, a special class of malware that hides its presence from the operating system and administrative tools. Other stealth mechanisms include:

• Stopping activities that are easy to detect when a new user logs in
• Using a Unix socket [howtogeek.com] over TOR for external communications
• Deleting its installation binary after execution and running as a background service thereafter
• Manipulating the Linux process pcap_loop through a technique known as hooking to prevent admin tools from recording the malicious traffic
• Suppressing mesg errors to avoid any visible warnings during execution.

The malware is designed to ensure persistence, meaning the ability to remain on the infected machine after reboots or attempts to delete core components. Two such techniques are (1) modifying the ~/.profile script, which sets up the environment during user login so the malware loads ahead of legitimate workloads expected to run on the server and (2) copying itself from memory to multiple disk locations. The hooking of pcap_loop can also provide persistence by allowing malicious activities to continue even after primary payloads are detected and removed.

Besides running using the machine resources to mine cryptocurrency, Perfctl also turns the machine into a profit-making proxy that paying customers use to relay their Internet traffic. Aqua Security researchers have also observed the malware serving as a backdoor to install other families of malware.

Assaf Morag, Aqua Security’s threat intelligence director, wrote in an email:

Perfctl malware stands out as a significant threat due to its design, which enables it to evade detection while maintaining persistence on infected systems. This combination poses a challenge for defenders and indeed the malware has been linked to a growing number of reports and discussions across various forums, highlighting the distress and frustration of users who find themselves infected.

Perfctl uses a rootkit and changes some of the system utilities to hide the activity of the cryptominer and proxy-jacking software. It blends seamlessly into its environment with seemingly legitimate names. Additionally, Perfectl’s architecture enables it to perform a range of malicious activities, from data exfiltration to the deployment of additional payloads. Its versatility means that it can be leveraged for various malicious purposes, making it particularly dangerous for organizations and individuals alike.

“The malware always manages to restart”

While Perfctl and some of the malware it installs are detected by some antivirus software, Aqua Security researchers were unable to find any research reports on the malware. They were, however, able to find a wealth of threads on developer-related sites that discussed infections consistent with it.

This Reddit comment [reddit.com] posted to the CentOS subreddit is typical. An admin noticed that two servers were infected with a cryptocurrency hijacker with the names perfcc and perfctl. The admin wanted help investigating the cause.

“I only became aware of the malware because my monitoring setup alerted me to 100% CPU utilization,” the admin wrote in the April 2023 post. “However, the process would stop immediately when I logged in via SSH or console. As soon as I logged out, the malware would resume running within a few seconds or minutes.” The admin continued:

I have attempted to remove the malware by following the steps outlined in other forums, but to no avail. The malware always manages to restart once I log out. I have also searched the entire system for the string "perfcc" and found the files listed below. However, removing them did not resolve the issue. as it keep respawn on each time rebooted.

Other discussions include: Reddit [reddit.com], Stack Overflow [stackoverflow.com] (Spanish), [freelancer.com] forobeta [forobeta.com] (Spanish), [freelancer.com]brainycp [brainycp.com] (Russian), [freelancer.com] natnetwork [natanetwork.com] (Indonesian), [freelancer.com] Proxmox [proxmox.com] (Deutsch), [freelancer.com] Camel2243 [camel2243.com] (Chinese), [freelancer.com] svrforum [svrforum.com] (Korean), [freelancer.com] exabytes, [exabytes.co.id]virtualmin, [virtualmin.com]serverfault [serverfault.com] and many others. [virtualmin.com]

After exploiting a vulnerability or misconfiguration, the exploit code downloads the main payload from a server, which, in most cases, has been hacked by the attacker and converted into a channel for distributing the malware anonymously. An attack that targeted the researchers’ honeypot named the payload httpd. Once executed, the file copies itself from memory to a new location in the /temp directory, runs it, and then terminates the original process and deletes the downloaded binary.

Once moved to the /tmp directory, the file executes under a different name, which mimics the name of a known Linux process. The file hosted on the honeypot was named sh. From there, the file establishes a local command-and-control process and attempts to gain root system rights by exploiting CVE-2021-4043, a privilege-escalation vulnerability that was patched in 2021 in Gpac, a widely used open source multimedia framework.

The malware goes on to copy itself from memory to a handful of other disk locations, once again using names that appear as routine system files. The malware then drops a rootkit, a host of popular Linux utilities that have been modified to serve as rootkits, and the miner. In some cases, the malware also installs software for “proxy-jacking,” the term for surreptitiously routing traffic through the infected machine so the true origin of the data isn’t revealed.

The researchers continued:

As part of its command-and-control operation, the malware opens a Unix socket, creates two directories under the /tmp directory, and stores data there that influences its operation. This data includes host events, locations of the copies of itself, process names, communication logs, tokens, and additional log information. Additionally, the malware uses environment variables to store data that further affects its execution and behavior.

All the binaries are packed, stripped, and encrypted, indicating significant efforts to bypass defense mechanisms and hinder reverse engineering attempts. The malware also uses advanced evasion techniques, such as suspending its activity when it detects a new user in the btmp or utmp files and terminating any competing malware to maintain control over the infected system.

The diagram below captures the attack flow:

The following image captures some of the names given to the malicious files that are installed:

By extrapolating data such as the number of Linux servers connected to the Internet across various services and applications, as tracked by services such as Shodan and Censys, the researchers estimate that the number of machines infected by Perfctl is measured in the thousands. They say that the pool of vulnerable machines—meaning those that have yet to install the patch for CVE-2023-33426 or contain a vulnerable misconfiguration—is in the millions. The researchers have yet to measure the amount of cryptocurrency the malicious miners have generated.

People who want to determine if their device has been targeted or infected by Perfctl should look for indicators of compromise included in Thursday’s post [aquasec.com]. They should also be on the lookout for unusual spikes in CPU usage or sudden system slowdowns, particularly if they occur during idle times. Thursday’s report also provides steps for preventing infections in the first place.

at-least-they-aren't-exploding dept.

11 million devices infected with botnet malware hosted in Google Play [arstechnica.com]:

Five years ago, researchers made a grim discovery—a legitimate Android app in the Google Play market that was surreptitiously made malicious [arstechnica.com] by a library the developers used to earn advertising revenue. With that, the app was infected with code that caused 100 million infected devices to connect to attacker-controlled servers and download secret payloads.

Now, history is repeating itself. Researchers from the same Moscow, Russia-based security firm reported Monday [kaspersky.com] that they found two new apps, downloaded from Play 11 million times, that were infected with the same malware family. The researchers, from Kaspersky, believe a malicious software developer kit for integrating advertising capabilities is once again responsible.

Clever tradecraft

Software developer kits, better known as SDKs, are apps that provide developers with frameworks that can greatly speed up the app-creation process by streamlining repetitive tasks. An unverified SDK module incorporated into the apps ostensibly supported the display of ads. Behind the scenes, it provided a host of advanced methods for stealthy communication with malicious servers, where the apps would upload user data and download malicious code that could be executed and updated at any time.

The stealthy malware family in both campaigns is known as Necro. This time, some variants use techniques such as steganography [wikipedia.org], an obfuscation method rarely seen in mobile malware. Some variants also deploy clever tradecraft to deliver malicious code that can run with heightened system rights. Once devices are infected with this variant, they contact an attacker-controlled command-and-control server and send web requests containing encrypted JSON [wikipedia.org] data that reports information about each compromised device and application hosting the module.

The server, in turn, returns a JSON response that contains a link to a PNG image and associated metadata that includes the image hash. If the malicious module installed on the infected device confirms the hash is correct, it downloads the image.

The SDK module “uses a very simple steganographic algorithm,” Kaspersky researchers explained in a separate post [securelist.com]. “If the MD5 check is successful, it extracts the contents of the PNG file—the pixel values in the ARGB channels—using standard Android tools. Then the getPixel method returns a value whose least significant byte contains the blue channel of the image, and processing begins in the code.”

The researchers continued:

If we consider the blue channel of the image as a byte array of dimension 1, then the first four bytes of the image are the size of the encoded payload in Little Endian format (from the least significant byte to the most significant). Next, the payload of the specified size is recorded: this is a JAR file encoded with Base64, which is loaded after decoding via DexClassLoader. Coral SDK loads the sdk.fkgh.mvp.SdkEntry class in a JAR file using the native library libcoral.so. This library has been obfuscated using the OLLVM tool. The starting point, or entry point, for execution within the loaded class is the run method.

Follow-on payloads that get installed download malicious plugins that can be mixed and matched for each infected device to perform a variety of different actions. One of the plugins allows code to run with elevated system rights. By default, Android bars privileged processes from using WebView, an extension in the OS for displaying webpages in apps. To bypass this safety restriction, Necro uses a hacking technique known as a reflection attack [wikipedia.org] to create a separate instance of the WebView factory.

This plugin can also download and run other executable files that will replace links rendered through WebView. When running with the elevated system rights, these executables have the ability to modify URLs to add confirmation codes for paid subscriptions and download and execute code loaded at links controlled by the attacker. The researchers listed five separate payloads they encountered in their analysis of Necro.

The modular design of Necro opens myriad ways for the malware to behave. Kaspersky provided the following image that provides an overview.

The researchers found Necro in two Google Play apps. One was Wuta Camera, an app with 10 million downloads to date. Wuta Camera versions 6.3.2.148 through 6.3.6.148 contained the malicious SDK that infects apps. The app has since been updated to remove the malicious component. A separate app with roughly 1 million downloads—known as Max Browser—was also infected. That app is no longer available in Google Play.

The researchers also found Necro infecting a variety of Android apps available in alternative marketplaces. Those apps typically billed themselves as modified versions of legitimate apps such as Spotify, Minecraft, WhatsApp, Stumble Guys, Car Parking Multiplayer, and Melon Sandbox.

People who are concerned they may be infected by Necro should check their devices for the presence of indicators of compromise listed at the end of this [securelist.com] writeup.

Original Submission