New Stealthy Shikitega Malware Targeting Linux Systems and IoT Devices
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2021-3493 | Linux Kernel overlayfs Local Privilege Escalation via User Namespace Flaw The overlayfs stacking file system in the Linux kernel does not properly validate the application of file capabilities against user namespaces, so capability checks can be bypassed when overlayfs is used inside a user namespace (CWE-862, missing authorization). A local attacker who can create user namespaces and mount an overlayfs filesystem can place a file with crafted file capabilities on that mount and execute it, gaining capabilities beyond their own namespace and escalating to root on the host. Any Linux deployment that enables unprivileged user namespaces with overlayfs support is affected; the flaw is specific to distribution kernels exposing this feature (known to affect Ubuntu builds), not every upstream kernel configuration. CISA added the vulnerability to its Known Exploited Vulnerabilities catalog on 2022-10-20, confirming exploitation in the wild, though no public proof-of-concept is catalogued in the source data and EPSS estimates a roughly 49% probability of exploitation within 30 days. Do: Apply updated kernel packages from your distribution per vendor instructions, as CISA's KEV entry requires, and reboot into the patched kernel (Ubuntu resolved this flaw in its July 2021 kernel security updates). As an interim mitigation, restrict or disable unprivileged user namespaces via system policy or sysctl and limit local access to trusted users. Verify the running kernel version after reboot, since the fix is not effective until the system boots the updated kernel. | 7.8 | 49% | KEV PoC ×2 |
| masshundreds of millions of Linux systems deployed overall, with the vulnerable subset (kernels exposing overlayfs via user namespaces, notably Ubuntu) plausibly… | |
| CVE-2021-4034 | Out-of-Bounds Read/Write Local Privilege Escalation in polkit pkexec (PwnKit) CVE-2021-4034 ('PwnKit') is an out-of-bounds read and write (CWE-125/CWE-787) in polkit's setuid-root pkexec utility, which mishandles the calling parameter count and ends up trying to execute environment variables as commands. A local attacker who runs pkexec with crafted environment variables can induce it to execute arbitrary code, gaining administrative (root) rights on the target machine. Because polkit is installed by default on mainstream Linux distributions — including Red Hat Enterprise Linux and its many variants, with the flaw also tracked against Canonical, SUSE, Oracle, Siemens, and StarWind Software products — essentially every standard Linux installation was exposed. The flaw is being actively exploited in the wild: CISA added it to the Known Exploited Vulnerabilities catalog on 2022-06-27 with known ransomware use, and EPSS assigns a 94.9% probability of exploitation (100th percentile). Public proof-of-concept exploits are widely available, making exploitation trivial for any user with local access to an unpatched host. Do: Apply the polkit/pkexec updates from each distribution vendor immediately per vendor instructions, as required by the CISA KEV catalog. If patching must be delayed, removing the setuid bit from pkexec (e.g., chmod 0755 /usr/bin/pkexec) is a widely documented interim mitigation, though it may affect functionality that relies on pkexec. Prioritize hosts where untrusted or low-privilege users can log in, and hunt for prior exploitation given known ransomware use. | 7.8 | 95% | KEV ransomware PoC ×4 |
| masstens of millions of Linux servers and workstations (polkit/pkexec ships by default on virtually all mainstream distributions) |
Full article423 words · extracted from thehackernews.com · click to collapse
Ravie LakshmananSep 07, 2022
A new piece of stealthy Linux malware called Shikitega has been uncovered adopting a multi-stage infection chain to compromise endpoints and IoT devices and deposit additional payloads.
"An attacker can gain full control of the system, in addition to the cryptocurrency miner that will be executed and set to persist," AT&T Alien Labs said in a new report published Tuesday.
The findings add to a growing list of Linux malware that has been found in the wild in recent months, including BPFDoor, Symbiote, Syslogk, OrBit, and Lightning Framework.
Once deployed on a targeted host, the attack chain downloads and executes the Metasploit's "Mettle" meterpreter to maximize control, exploits vulnerabilities to elevate its privileges, adds persistence on the host via crontab, and ultimately launches a cryptocurrency miner on infected devices.
The exact method by which the initial compromise is achieved remains unknown as yet, but what makes Shikitega evasive is its ability to download next-stage payloads from a command-and-control (C2) server and execute them directly in memory.
Privilege escalation is achieved by means of exploiting CVE-2021-4034 (aka PwnKit) and CVE-2021-3493, enabling the adversary to abuse the elevated permissions to fetch and execute the final stage shell scripts with root privileges to establish persistence and deploy the Monero crypto miner.
In a further attempt to fly under the radar, the malware operators employ a "Shikata ga nai" polymorphic encoder to make it more difficult to detect by antivirus engines and abuse legitimate cloud services for C2 functions.
Shikitega is also indicative of a trend toward malicious actors expanding their attack reach to accommodate the Linux operating system that's widely used in cloud platforms and servers across the world, contributing to a surge in LockBit and Cheerscrypt ransomware infections.
According to Trend Micro 2022 Midyear Cybersecurity Report, "the emergence of these new Linux ransomware families directly corresponds to [...] a 75% increase in ransomware attacks targeting Linux systems in the first half of 2022 compared to the first half of 2021."
"Threat actors continue to search for ways to deliver malware in new ways to stay under the radar and avoid detection," AT&T Alien Labs researcher Ofer Caspi said.
"Shiketega malware is delivered in a sophisticated way, it uses a polymorphic encoder, and it gradually delivers its payload where each step reveals only part of the total payload."
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Text extracted automatically; images, tables and formatting may be missing. Original: https://thehackernews.com/2022/09/new-stealthy-shikitega-malware.html