The reason why many countries want travelers to have at least 6 months validity left on there passports is those same countries generally allow visiting tourists to extend their stays in that country for up to 6 months. If that were to happen, they want to make the visitor's passport will still be valid so they will be able to leave when their visitor's visa expires.

One can never predict what a particular "Immigration Official" may do on any given day but since you have an onward tickets and your passport will be valid for almost 6 month after your planned departure it is doubtful you will have any kind of problem regarding the expiration date of your passport during any leg of your trip.

Airlines are supposed to forestall these kinds of issues by not allowing visitors onto planes if their passports don't meet the entry requirements of the country to which they are traveling. So I think it's much more likely that you will not be allowed on the plane to KL in the first place. In that case you'd probably be liable for buying a new ticket or at the very least paying the change fee for your ticket (if that is even allowed by your airline).

The only exception I can see is if Malaysia considered you still "in transit" and granted you a 48-hour visa. Some countries do that or will just give you a very short visa period. In that case, you'd probably be required to show your airline tickets. But I wouldn't count on that.

Singapore, for example, is very strict and simply won't make exceptions. I'm not sure about Malaysia.

I would look up what each country's foreigh affairs department says.
I have travelled often with less 6 months on my passport but always check the arrival country's requirement first. eg I travelled to US with less than 6 months left on passport but this is not permitted for UK -I have an Australian passport. The airlines don't always give accurate inforamtion about this so double check.

Malaysia requires 6 months, Oz requires the passport to be valid on the day you leave but you must apply for an ETA in advance. Airlines however may impose their own rules.

http://travel.state.gov/travel/cis_pa_tw/cis/cis_960.html#entry_requirements
http://travel.state.gov/travel/cis_pa_tw/cis/cis_954.html#entry_requirements

but this is not permitted for UK

THAT is surprising as generally the UK just requires to have the passport valid on the day of leaving the UK - and that is the norm for all visitors not just ones who can obtain a visa on arrival.

Great thanks for all your replies. Much appreciated.
I think I will take the risk and see what happens.
@alanRow - How do I apply for a ETA?

If I am reading this correctly, jmath, you don't need an ETA for Australia because you are Australian. The ETA is the electronic visa non-Australians need to enter the country.

alanRow-OP has an Australian passport and this info is for US citizens

"generally the UK just requires to have the passport valid on the day of leaving the UK - and that is the norm for all visitors not just ones who can obtain a visa on arrival."

The UK requires visitors requiring a visa (which doesn't include ordinary Australian or US tourists) to have six months on their passport when they arrive in Britain.

This is actually to allow deportation of overstayers (some countries might not allow overstayers back in if their passport's invalid) and really is designed for people from dodgy countries. But rules is rules, and there are lots of reasons (like working here) Northie, though Australian, might have needed a visa to visit Britain.

Northie's probably accurate in saying Northie needed six months' passport validity. He's mistaken in inferring from this that other Australians would be in the same position.