frankthedm said:
An Awakened animal suffers those issues. A temp boost might not need such dire concequences unless some Rules Rapist is going to try and claim said animal now understands common.
"Rules Rapist"?
Seriously - Fox's Cunning is a 2nd level spell, and animal companions aren't known for having intelligence-based skills; this will basically have no other meaningful effect. Meanwhile, Speak With Animals is on the Druid list, has the same duration, and is a 1st level spell. This hardly merits strong language; it's not exactly overpowered here.
As Fox's Cunning is not a Druid spell, it's more likely that a hostile Wizard will want to cast it on the opposing druid's companion, then claim it now understands common, in order to get "dire consequences" for the opposing Druid (or at least, be warned that this may happen the next time you have a BBEG Druid if you've put dire consequences onto the PC Druid for having this happen).
If we want to get silly, cast Tongues (cleric-4) on the animal companion. No rules-bendery at all (it explicitly states it grants the ability to understand and speak all languages of intelligent creatures, and makes no restrictions on what kind of creature it can affect), and now, not only does it understand common (and Celestial, and Fiendish, and Dwarven, and Elven, and...), but it can also speak it (and Celestial, and Fiendish, and Dwarven, and Elven, and...).