Guessing the key in AES256-GCM? I assume that my case is weird but I've the following information:


IV: 0x263e or 0x3e26
Auth tag: 0x25
AES256-GCM encrypted payload: 0x4eec96df534ade4c013a
AES256-GCM decrypted payload: 0x0041e36baf2648090174


Regarding the length of the IV and Auth tag, I'm wondering if it is possible to guess the key used to encrypt the payload ?
No.

The short authentication tag makes for high probability of forgery.  But that's not relevant here.

The short nonce limits the number of messages that can safely be encrypted with the same key—indeed, narrowing it down to two possibilities limits it to two messages.  But you have only one message.

What's left is breaking AES.  Good luck!