expression, i-adjective
out of control; unmanageable; out of hand
Idiomatic expression describing a situation or person that has become uncontrollable, often with a negative connotation. Similar to 手がつけられない, but uses の instead of が, which is a common variation.
See also: 手がつけられない (てがつけられない)
His anger was out of control.
部屋が手の付けられないほど散らかっている。
The room is so messy it's unmanageable.
Same meaning; 手の付けられない is a variant with の instead of が, both are idiomatic and interchangeable.
From 手 (hand, means of control) + の (possessive particle) + 付けられない (negative potential form of 付ける, to attach, to handle). Literally 'cannot attach a hand to it', meaning something is beyond one's ability to manage.