What is the punishment of one who kissed an alien woman in Ramadan?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

It is forbidden to kiss a non-Mahram woman (alien), as that is one of the reasons that could lead to fornication and adultery.

If that happens during Ramadan, then the sin is greater.  At times of superiority and excellence, the sin is more serious than at other (ordinary) times.

Whoever has committed a sin has to repent Allah before it is too late for him.

True repentance implies staying away from circumstances of committing that sin, and performing many good deeds, especially optional prayers. 

It is reported in Saheeh Bukhari and Muslim that Ibn Masoud narrated that "A man kissed a woman. He came to the Prophet (Sallallahu Alaihi wa Sallam) and told him what had happened. Then the following verse was revealed: {And perform As-Salât (Iqâmat-as-Salât), at the two ends of the day and in some hours of the night [i.e. the five compulsory Salât (prayers)]. Verily, the good deeds remove the evil deeds (i.e. small sins). That is a reminder (an advice) for the mindful (those who accept advice).}.  The man said: ‘Has this verse been revealed in relation to me only, Oh! Prophet (Sallallahu Alaihi wa Sallam) of Allah? The Prophet (Sallallahu Alaihi wa Sallam) replied: “For whoever acts upon it from my Ummah.”

As regards the ruling regarding Ramadan, if the kissing took place during the day in Ramadan, the fasting is correct unless there is an ejaculation of sperm, in which case the fasting becomes invalid, and one has to make it up.

In case the kissing took place other than during the time of fasting, then it does not affect the validity of fasting in any case.

We draw your attention to the fact that what we have mentioned in relation to the ruling about the validity of the fasting not its reward.  In fact, reward of fasting was surely affected.    The Prophet (Sallallahu Alaihi wa Sallam) said: "Allah does not need the fast of one who does not abandon false speech or acting according to his false speech.” [Reported by Imam Bukhari]

Allah knows best.