‘Foreigners of non-ASEAN countries are not legally allowed to work in most of Southeast Asia without a valid work permit, and so working in exchange for food and accommodation cannot be considered paid work. All of the advice below pertains specifically to travelling as a tourist as most volunteers must enter a country only as a tourist. This is unless you have official documentation from a registered NGO which allows you to apply for a ‘special visa’ and stay for a longer period of time.’
Visa Guide for Volunteers, WWOOFERS & HelpStayers to Southeast Asia (southeastasiabackpacker.com)
In addition to the preceding link, VSEA is working toward providing specific information regarding the legality of volunteer work in each country we have listed, including whatever application procedures are needed to ensure government approval.
This information will be provided at the relevant country page under the LOCATION tab e.g. INDONESIA | VOLUNTEER SOUTH EAST ASIA