According to many authentic narrations, the Prophet (Sallallahu alaihi wasallam) prohibited the eating of every fanged predator (carnivores/beasts of prey):
عَنْ ابْنِ عَبَّاسٍ : أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ " نَهَى عَنْ كُلِّ ذِي نَابٍ مِنَ السِّبَاعِ وَعَنْ كُلِّ ذِي مِخْلَبٍ مِنَ الطَّيْرِ "
Translation: Ibn Abbas (r.a.) narrates that the Messenger of Allah (Sallallahu alayhi wasallam) forbade the eating of every fanged beast of prey and all the birds having talons. (Sahih Muslim)
The fox is an animal included in the list of fanged beasts of prey which are explicitly forbidden to eat. Notice that the word Kull is used in the Hadith, meaning “every” and “all”. Therefore, there are no exceptions whatsoever to this law of the Shari'ah. It is sad that many Muslims consider the "four schools of thought - Hanafi, Maliki, Shafi'ie, and Hanbali" to be infallible by blindly following them when they have so many rulings within them that clearly go against the divine Revelation.
For example, Imam Shafi'ie, to whom the Shafi'ie school of jurisprudence is attributed, said:
وَتُؤْكَلُ الضَّبُعُ وَالثَّعْلَبُ
Translation: “It is allowed to eat the hyena and the fox”
Reference: Kitab ul Umm; vol.2, p.628