The US does not currently have a legal permission to be in Ukraine. Ukraine does not have a defense agreement with the US that could land troops, Ukraine is not a NATO member, so forth. Right now, for the US to cyberattack Russia would be a direct act of war and quite literally cause the Cold War to become the Hot War.
For this reason, just like how our troops are not in Ukraine but in surrounding countries watching, our NSA hackers are most likely standing down as well, as tragic as it may be.
The US and Russia agreed to defend Ukraine after Ukraine agreed to give up its nuclear weapons in the 1994 Budapest Memorandum. The Russians are violating this agreement today, and the US would be following it to defend Ukraine from Russia’s invasion.
When the Budapest Memorandum was signed, having one of the defenders be the invaders was not expected.
As a result, even if that binding is still in power, is it worth defending Ukraine by going to war against Russia? That would literally start World War III. Letting Ukraine fall is terrible, awful, painful - but it's better than WWIII.
For this reason, just like how our troops are not in Ukraine but in surrounding countries watching, our NSA hackers are most likely standing down as well, as tragic as it may be.