Which one? There are two suburbs called Clichy north of Paris:
1 - Clichy la Garenne right outside Paris in the Hauts de Seine département.
2 - Clichy-sous-Bois further east-north east of Paris, in the infamous Seine-St-Denis département.
Actually I don't know why I ask which one since the answer is yes for both:
1 - Clichy la Garenne ranks as the 8th most violent city in France when it comes to Assault & Battery and Robbery. For these two types of violent crime, the rate is 14.72 for 1,000 people, which is 2.5 times the national average.
2 - Clichy-sous-Bois is where the November 2005 general riots started. Crime rate for this town alone is not available because it is part of the police constituency of another town called Le Raincy, which is one of the few relatively safe and posh towns in the Seine St-Denis département. The combined Assault& Battery and Robbery rates in this constituency is 9.96 for 1,000 people. Considering that other suburbs similar to Le Raincy have rates closer to 4, I suspect Clichy-sous-Bois to have an even higher crime rate than the other Clichy. It has a nationwide reputation of being one of the most dangerous places in France.
These rates do not take into account other categories of violent crime so you can imagine the total violent crime and total crime rates are pretty high. Add the fact that half the victims do not report it to the police and that this rate is even higher in this type of neighborhood.
Like in all dangerous cities you have some parts of town that are not too bad but as a whole, yes, they are both rather unsafe.
Edit: Métro Mairie de Clichy is in Clichy la Garenne, right outside Paris. It's not a bad métro line overall. I don't know Clichy personally so I could be wrong but as far as I know this particular district is not the bad part of town.
2nd Edit: just read Bradwell's message: the youth hostel is definitely in Clichy la Garenne so if you are going there you should be fine. But what doesn't seem dodgy to a guy may feel different to a girl and I deduct from your name that you must be a girl. Just stick to busy areas and you'll be fine but remain aware of your surroundings at all times.