
Samsung Galaxy Ace DUOS
Every official firmware build for GT-S6802, newest first: one row per build with all regions (CSC) that received it.
Each firmware build has its own page at https://samfirm.shop/build/{PDA}, where {PDA} is the build number from the list above. Example: https://samfirm.shop/build/S6802XXNI1
Box codes of GT-S6802 for different colors and markets. Firmware is chosen by the model code GT-S6802 and your region (CSC), not by the SKU.

GT-S7508

GT-S7500T

GT-S6812

GT-S6500L

GT-S5690L

GT-S5670

GT-S5570I

GT-S5303
You can find the firmware on the model: GT-S6802 page.
Yes, all firmware files for GT-S6802 are 100% official, original, and obtained directly from Samsung servers.
To flash GT-S6802, you need to download the appropriate firmware, put your device into Download Mode, and use the Odin tool to load the BL, AP, CP, and CSC files.
Downgrading is only possible if the bootloader version (binary bit) of the old firmware matches the current one. Always check the binary version before flashing GT-S6802.