How to recover apps password in R12.

In R12 , apps password is not hardcoded, still few workarounds may work for you.
1. if sqlplus , than u need to set it back to old value and continue to work. you can also use 'identified by value' option instead of giving password.

2. if FNDCPASS , than
a. You  can change it back to old value...no loss.
b. if you have any custom program which has apps password hardcoded u can check from there.
c. if you have any custom script in cron or so where apps password is hardcoded u can check from there.
d. check bash_history for last FNDCPASS command.
   e.
Decrypting APPS password in R12 :
SQL> show user
USER is "SYS"
SQL> create FUNCTION apps.decrypt_pin_func(in_chr_key IN VARCHAR2,in_chr_encrypted_pin IN VARCHAR2)
RETURN VARCHAR2
AS
LANGUAGE JAVA NAME 'oracle.apps.fnd.security.WebSessionManagerProc.decrypt(java.lang.String,java.lang.String) return java.lang.String';
/ 2 3 4 5

Function created.

SQL> select ENCRYPTED_FOUNDATION_PASSWORD from apps.fnd_user where USER_NAME='GUEST';

ENCRYPTED_FOUNDATION_PASSWORD
--------------------------------------------------------------------------------
ZG1040180FF7A514EB0209759D297661E8E28DD99460D28850C00D783E24843FC44BCB81BD289305AA4FCFF468533FBBBB72


SQL> SELECT apps.decrypt_pin_func('GUEST/ORACLE','ZG1040180FF7A514EB0209759D297661E8E28DD99460D28850C00D783E24843FC44BCB81BD289305AA4FCFF468533FBBBB72') from dual;

APPS.DECRYPT_PIN_FUNC('GUEST/ORACLE','ZG1040180FF7A514EB0209759D297661E8E28DD994
--------------------------------------------------------------------------------
S2MUL8TION

SQL> conn apps/S2MUL8TION
Connected.
SQL>

SQL> drop function apps.decrypt_pin_func;

Function dropped.