I am professional web developer and got a contract to fix a pub site. Is it permissible to fix this site, or not?
It does not mean if you don't consume there products that makes it okay for to assist them in making available to others, wehter its directly or indirectly.
Take for example the following: its like saying my friend is a drug dealer I can help him by dropping him to his dealing location, although you didn't sell or consume the drugs with him but you still helped in the process!
this is just logic speaking, but the hadith below is also another justification: Imam Ahmad recorded that Ibn `Umar said that the Messenger of Allah said,
«لُعِنَتِ الْخَمْرُ عَلى عَشْرَةِ أَوْجُهٍ: لُعِنَتِ الْخَمْرُ بِعَيْنِهَا، وَشَارِبُهَا، وَسَاقِيهَا، وَبَائِعُهَا، وَمُبْتَاعُهَا، وَعَاصِرُهَا، وَمُعْتَصِرُهَا، وَحَامِلُها، وَالْمَحْمُولَةُ إِلَيْهِ، وَآكِلُ ثَمَنِهَا»
(Ten matters related to Khamr were cursed. Khamr itself was cursed, whoever drinks it, its server, seller, buyer, brewer, who asks for it to be brewed, whoever carries it, whomever it is carried to and whoever consumes its price.)
You have to be careful in these situation because shaytan will tempt you to think of it being halal or come up with some justification:
Allah (SWT) says, "He [Satan] said: Give me respite until the day they are raised up. [Allah] said: You are among those allowed respite. He [Satan]said: Because You have thrown me out (Of the Way), lo !, I will sit waiting for them, on Your straight path, then I will come in from before them and behind them, from their right and from their left and you will not find most of them Gratitude (for Your Mercies) ." [Quran 7:14-171]
us as Muslims we have evaluate what is good and what is bad, those evaluated and turned out to be bad are forbidden, just because something in the Quran is not excplicitly mentioned you can't assume that its halal!
salaam, doing any haram act or helping in it is haram, like this work. you must use your ability in halal ways.