Factual error: In the scene at the race track where they show the virus infecting and destroying cells in the blood stream, they clearly show that it is red blood cells being infected. Viruses, in order to replicate, require the cell's DNA replication machinery. However, mature red blood cells in the circulation no longer possess this machinery since they no longer have a nucleus or DNA. It would therefore be impossible for this virus to replicate.
Factual error: In the scene where Ethan is in the helicopter about to rappel into the BioCyte building, you see his hair blowing upward. In reality, the prop wash from the helicopter would make his hair blow into his face.
Factual error: The car chase between Ethan and Nyah is supposed to take place in Spain involving Spanish cars (plate's colour and the way numbers and letters are represented follows the Spanish code), but a real Spanish plate should have numbers and letters displayed as follows '1234 ABC' or 'AB- 1234-AB'.
Factual error: The portrait of Semana Santa (Eastern) celebrations in Sevilla are absurd. Weird wooden constructions on fire (I guess it refers to Fallas, a celebration from Valencia and Alicante, around 400 miles away, in a tradition in which people burn cheap satirical and arty polystyrene sculptures with the arrival of Spring). Repetitive satanic hymns, fantasy castles, ritual drums, fireplaces and candles everywhere, effigies on sticks on flames, traditional clothes from somewhere in Central America mixed with San Fermín outfits and flutes (from Pamplona, over 600 miles away), frantic dances and women throwing flower petals over the crowd. I only miss some bulls dancing around in flamenco clothes while drinking sangría. The equivalent would be to portray a US festival in which Mickey Mouse rides a horse wearing a scary pumpkin mask while being carried by a leprechaun watching fireworks.
Factual error: The aeroplane at the beginning of the film is a 747-400. You can tell because the wings had winglets when they showed the exterior view. Well, a 747-400 only has a two man cockpit, there is no "sideways flying" flight engineer like in the movie.
Factual error: Near the end, Ethan Hunt and Sean Ambrose engage in a high-speed motorcycle chase that culminates with them crashing their motorcycles head-on. Just before the crash, both men leap off their bikes and their bodies collide in mid-air above the crash. However, if Hunt and Ambrose were racing towards each other at 40 mph (a conservative estimate), then the combined force of their bodies colliding would be equivalent to an 80 mph impact, which would pulverize their skeletons and kill both men instantly.
Factual error: During the motorcycle chase gasoline spills from the bullet hole on the motorcycle. Every mechanic knows that gas doesn't have drops like those, it spreads out in a thin film. Also the wind would blow it away.