MD5 - Chosen Prefix Collision Attack
The answer is due to the Stevens et. al's work ;

Chosen-prefix collisions for MD5 and applications,  2012.

They showed that, with an approximately $2^{39}$ calls to the MD5 compression function, it is possible, for any chosen $m_1$ and $m_2$, to construct $s_1$ and $s_2$ such that $$\text{MD5} (m_1\mathbin\|s_1) = \text{MD5} (m_2\mathbin\|s_2)$$
They also gave examples for colliding documents, software integrity checking, etc ...