https://www.gov.uk/foreign-travel-advice/france/safety-and-security

Terrorism in France
Terrorists are very likely to try to carry out attacks in France.

There can be frequent industrial action across France. This can lead to disruption and delays on roads and public transport. If you're due to travel to or within France, monitor the media, check your operator's advice and follow the advice of the authorities.

Thieves and pickpockets operate on the Paris Métro, on RER (train) lines and at mainline stations.

Assaults
There have been several cases of serious assault on the RER line B, which serves:
Paris Charles de Gaulle airport
Orly Airport
Paris Gare du Nord Eurostar terminus
There have also been serious assaults on RER line D, which serves the Stade de France.
un sentiment d'insécurité AYAAAA