Right now Tika 1.2 uses ASM 3.1.
However this is causing some issues for us on the XWiki project since we also bundle other framework that use a more recent version of ASM (we use pegdown which uses parboiled which draws ASM 4.0).
The problem is that ASM 3.x and 4.0 are not compatible...
See http://jira.xwiki.org/browse/XE-1269 for more details about the issue we're facing.
Thanks for considering upgrading to ASM 4.x