Wa Alaikumus Salam Wa Rahmatullah,
In theory, Kosher meat is Halal for Muslims to eat because Allah has said in Qur'an "وطعام الذين اوتوا الكتاب حلّ لكم" the meaning of which is" And the food of people of scripture is Halal (permissible) for you".
The people of book includes Jews and Christians and by what is implied by food is meat according to exegetists of Qur'an.
The problem in practical matters is that it is very difficult to ensure that the Halal animal was slaughtered by a Jew or Christian properly while fulfilling their religious requirements of slaughter. Like Muslims, Jews and Christians are required to follow certain religious requirements regarding their slaughter as well. If they fulfill those religious requirements then their slaughter will be Halal for Muslims and if they do not observe those conditions then their slaughter will not be Halal for Muslims.
Jews have proven follow their rituals of slaughter more strictly than Christians but still it is difficult to know precisely whether the laws were observed or not.
If there is a Kosher brand whose authenticity is established beyond doubt then there it would be permissible to eat such Kosher meat.
And Allah knows best.
Mufti Ikram ul Haq
Fatwa Center of America