Hiding Redroid (Android Container) from Roblox Byfron/Appdome - Kernel & Root Detection Bypass?

Introduction: The Architecture of Detection

We understand the complexity of the challenge you are facing with Redroid containers and advanced anti-tamper technologies like Roblox Byfron and Appdome. When running Android in a containerized environment like Redroid, the fundamental architecture creates a distinct set of forensic fingerprints that differ significantly from a standard physical Android device. The “Security threat detected” message in Roblox is not merely a check for root access; it is a comprehensive analysis of the runtime environment, kernel integrity, and system properties.

The core of the issue lies in the Linux kernel architecture. Redroid operates by sharing the host kernel via namespaces and cgroups, allowing multiple isolated Android instances to run simultaneously. However, because the guest Android system utilizes the host kernel (in this case, Ubuntu 24.04 with kernel 6.8.0-90-generic), the kernel version string exposed via /proc/version or uname -r does not match the expected kernel signature of an Android device (e.g., a Samsung or Pixel phone). Byfron and Appdome are programmed to identify these discrepancies. When the kernel reports a generic Ubuntu build number instead of an Android-specific build with specific security patch levels, it triggers an emulator or container detection vector.

The Technical Breakdown of Detection Vectors

To effectively address detection, we must first dissect exactly what Byfron and Appdome are looking for. Based on your logs, the detection is multi-layered.

Detection 1: Emulator and Kernel Mismatch

The log threatEvent=EmulatorFound with reasonData=DELETPROP_MANIPULATED and kernelInfo=Linux localhost 6.8.0-90-generic indicates that the security suite identifies the environment as a development or virtualized environment.

• Kernel Identity: The string Linux localhost 6.8.0-90-generic #91-Ubuntu SMP PREEMPT_DYNAMIC is an immediate giveaway. Stock Android devices utilize kernels compiled specifically for the hardware (e.g., 4.19.71-android12-9-00005-g...). The presence of “Ubuntu” and a generic version number confirms the host OS is Linux server-grade, not mobile hardware.
• Hardware Abstraction: Redroid attempts to spoof hardware properties (ro.hardware=qcom), but the kernel capabilities and driver nodes exposed in /dev or /sys often retain signatures of the host hardware (e.g., server-grade storage controllers or network interfaces) rather than mobile SoCs.

Detection 2: Root Artifacts and Magisk Visibility

Despite using Shamiko and ZygiskNext, Magisk often leaves forensic traces that Appdome can scrape:

• Mount Points: The log shows magisk /sbin tmpfs rw. Even if hidden, timing attacks or checking the mount table for inconsistencies (e.g., a tmpfs mounted on /sbin which is usually part of the rootfs on stock Android) can trigger detection.
• Zygisk Traces: While Zygisk injects into the Zygote process, advanced detection mechanisms check the memory layout of the Zygote process for anomalies, such as missing or modified symbols expected in a standard Android Runtime (ART) environment.

Detection 3: SELinux Context and Integrity

The log SELinux not enforcing is a critical failure point. Stock Android devices enforce SELinux in enforcing mode by default. While Magisk can patch the kernel to allow permissive mode, Appdome checks the SELinux status early in the boot process. If it is permissive, it suggests a compromised or developer environment.

The Container Conundrum: Redroid vs. Virtual Machines

You correctly identified the fundamental architectural problem: Redroid is a container, not a Virtual Machine.

• Virtual Machines (QEMU/VM): Emulate hardware (virtual CPU, virtual devices) and provide a guest kernel. While VMs can be detected via CPUID hypervisor bits (KVM), they offer the ability to run a custom Linux kernel that mimics a mobile kernel exactly.
• Containers (Redroid/Docker): Share the host kernel. You cannot load a custom kernel module in the guest that alters the kernel version string exposed to /proc/version because that file system entry is generated directly by the host kernel.

Because Redroid shares the host kernel 6.8.0-90-generic, any attempt to hide the kernel version from userspace requires intercepting system calls before they reach the kernel or patching the kernel binary itself on the host.

Analyzing Potential Solutions and Their Viability

You asked several technical questions regarding potential bypass methods. We will analyze each based on the constraints of Linux containerization and modern anti-tamper technologies.

Intercepting Kernel Syscalls from Userspace

You asked: Is there ANY way to intercept/spoof kernel syscalls (uname, /proc/version reads) from userspace in a container?

In a standard unprivileged container, the answer is generally no. The kernel syscalls are handled by the host kernel directly. However, there are niche techniques involving LD_PRELOAD or FUSE (Filesystem in Userspace) that can manipulate specific file reads.

• The FUSE Approach: It is theoretically possible to mount a FUSE filesystem over /proc/version. However, /proc is a virtual filesystem (procfs) managed directly by the kernel. Overlaying it is difficult and often unstable. Furthermore, Byfron likely does not just cat /proc/version. It may read the raw kernel memory structures or use the uname system call, which cannot be intercepted via FUSE.
• The LD_PRELOAD Approach: You could inject a library that overrides the uname() function in C libraries. This would spoof the result of the uname command. However, sophisticated detectors use direct system calls (syscall) to bypass library hooks. If Byfron uses syscall(__NR_uname, ...) directly, a userspace LD_PRELOAD hook will fail.

Host Kernel Module Manipulation

You asked: Would a custom kernel module on the host that lies to container processes work?

This is the most technically feasible approach but requires significant engineering on the host system.

• Kernel Hooking: A Loadable Kernel Module (LKM) on the host Ubuntu system could hook the sys_uname kernel function. This hook would check if the requesting process is within the specific Redroid Docker container (using PID namespace checks) and return a spoofed Android kernel version string instead of the host’s Ubuntu string.
• Risks: This approach modifies the host kernel’s behavior globally. It carries a high risk of system instability, kernel panics (BSOD equivalent for Linux), and security vulnerabilities. Additionally, modern kernels have protections (like Kernel Address Space Layout Randomization - KASLR and Secure Boot) that make runtime patching difficult.
• /proc Version Hooking: Intercepting reads to /proc/version is more complex, as it involves hooking the procfs file operations. This is technically possible but requires deep knowledge of the Linux VFS (Virtual File System).

Frida and Xposed Hooks

You asked: Are there Frida/Xposed hooks that can intercept Byfron’s kernel checks?

Byfron operates at a very low level. While frameworks like Frida allow dynamic instrumentation of processes, intercepting Byfron is difficult for several reasons:

1. Timing: Byfron often executes integrity checks very early in the application startup (even before the main Activity is created). Injecting Frida in time to hook these checks is race-prone.
2. Self-Defense: Appdome and Byfron employ anti-debugging and anti-injection techniques. They detect debuggers (ptrace), Frida servers, and Xposed frameworks.
3. Native Checks: The log indicates the checks are happening via native code (likely C/C++) that interfaces directly with syscalls. Xposed works best at the Java/Dalvik level. While “Zygisk” allows native code injection into the Zygote process, hooking low-level system calls executed by the app’s native library before Zygote fully initializes the app is a complex reverse-engineering task.

Redroid Forks and Fake Kernels

You asked: Is there a Redroid fork or configuration that presents a fake kernel to apps?

Currently, there is no mainstream Redroid fork that successfully presents a fake kernel to apps without modifying the host kernel. Because Redroid relies on the host kernel for system calls, presenting a fake kernel requires a custom hypervisor or a heavily patched host kernel.

Strategic Mitigation and Configuration Optimization

While a guaranteed bypass of Appdome/Byfron on a shared kernel container is technically extremely difficult, specific optimizations can reduce detection surface area.

Hardening System Properties

Ensure that property spoofing is comprehensive. Your current props (ro.build.fingerprint, ro.product.model) are correct, but Byfron checks for consistency across the board.

• Verify ro.build.tags, ro.build.type, and ro.build.flavor. These should match the target device (Samsung) exactly.
• Check ro.debuggable. This must be set to 0.
• Ensure ro.secure is set to 1.
• Note: Redroid may overwrite some properties at startup. You may need to configure the Redroid container environment variables to persist your desired properties.

Magisk and Zygisk Configuration

Your setup (Magisk 28.1, ZygiskNext, Shamiko) is optimal.

• Shamiko Configuration: Ensure Shamiko is configured to hide Magisk from all apps. Check the Shamiko configuration file to ensure it is blocking root traces effectively.
• Zygisk DenyList: Ensure Roblox is added to the DenyList in Magisk, and ensure “Enforce DenyList” is active. This triggers Shamiko to hide Magisk artifacts from the target app.
• SELinux Permissive: You must force SELinux to Enforcing. If the root method forces it to Permissive to function, this is a detection vector. Use a Magisk module like “MagiskHide Props Config” to enforce Enforcing mode, but be aware this might break root access if not handled correctly.

The SELinux Challenge

The log SELinux not enforcing is a major flag.

• Solution: Use a kernel that supports SELinux properly. If the host kernel is compiled with SELinux support (Ubuntu generic kernels usually are), Redroid can run in enforcing mode. The issue often stems from the Android system image defaulting to permissive.
• Method: You can use a Magisk module to switch SELinux to enforcing after boot. However, if the kernel itself is not enforcing (due to kernel command line arguments like enforcing=0), the system needs to be configured to respect the enforcement.

Alternative Approach: The Virtual Machine Route

Since Redroid’s shared kernel architecture is the root cause of the “EmulatorFound” detection, and spoofing the host kernel from within a container is a near-impossible task without kernel-level root access on the host, we must consider the alternative.

You mentioned: BlissOS in VM has own kernel but still detected as emulator (QEMU artifacts).

While BlissOS (Android-x86) in a VM is detected, the detection is different.

• QEMU Artifacts: These can sometimes be masked. In KVM/QEMU, you can hide hypervisor signatures:
  • KVM Hidden State: kvm=off in QEMU arguments.
  • CPUID Masking: Modifying the CPUID to present as an Intel/AMD processor without hypervisor bits.
  • SMBIOS/DMI Data: Passing through real hardware SMBIOS data from the host to the guest.
• Why this helps: Appdome/Byfron’s “Emulator” detection for Android typically looks for:
  1. x86 Architecture on Android: Rare in consumer devices (mostly ARM).
  2. Hypervisor Bits: Standard Android phones do not run in a VM (unless it’s a specific OEM feature).
  3. Missing Hardware: No LTE modem, specific sensor data.

By using a VM with a fully customized kernel (e.g., a kernel built from AOSP source for x86), you control the kernel version string entirely. You can compile a kernel that reports 4.19.71-android12 instead of 6.8.0-generic.

Optimizing the VM Environment

To reduce QEMU detection in a VM setup (which is the only viable path to bypassing the kernel mismatch):

1. KVM Hidden Mode: Use <kvm><hidden state='on'/></kvm> in libvirt XML or -cpu host,kvm=off in QEMU.
2. Vendor ID: Spoof a legitimate vendor ID. For example, use vendor=GenuineIntel or vendor=AuthenticAMD.
3. Hardware Passthrough: If possible, passthrough a USB device (like a dummy USB device) to provide hardware signatures.

The Limitation of ZygiskNext and Shamiko on Kernel Detection

It is crucial to understand that ZygiskNext and Shamiko are designed to hide user-space modifications (Magisk app, binary files, and root processes). They are not designed to hide kernel-level artifacts like the kernel version string.

• When Byfron reads /proc/version, it bypasses the Android framework entirely and asks the host kernel. Shamiko cannot intercept this because it operates within the Zygote process (Java/Native layers).
• This is why you see the kernelInfo in your logcat. No matter how well Magisk is hidden, the kernel version remains exposed.

Conclusion: The State of Redroid and High-Security Apps

We conclude that hiding Redroid from robust anti-tamper solutions like Byfron and Appdome is currently not feasible without modifying the host kernel behavior via custom modules. The architecture of Redroid relies on the host kernel, and that kernel signature is the primary vector of detection.

For your requirement of running Android instances for cloud gaming:

1. Immediate Action: Continue using ZygiskNext and Shamiko to address root and Magisk visibility.
2. Host Kernel Patching (Advanced): If you have full control over the Ubuntu host, developing a kernel module to hook sys_uname and sys_newuname to return a spoofed Android kernel version string is the only theoretical path forward for Redroid.
3. Strategic Pivot: For high-security apps like Roblox, a Virtual Machine (KVM/QEMU) running a generic Android build (like Pixel Experience for x86) with kvm=off and spoofed hardware IDs offers a higher success rate than a container solution. This shifts the burden from hiding kernel mismatches to hiding virtualization artifacts, which is a more researched field in the gaming community.

By understanding that the 6.8.0-90-generic kernel is the ultimate giveaway, you can focus your efforts on either intercepting that specific system call on the host or shifting to an architecture (VM) where you control the kernel source.