Wikipedia – Can a Normal User Flag an Edit as Potential Vandalism?

You don't "flag" edits, per se. If you see an edit that is vandalism, you're expected to "rollback" or, at least, edit out the vandalism bits yourself. That's part of Wikipedia's mantra of Be Bold!

From http://en.wikipedia.org/wiki/Help:Content

You can edit almost any page on Wikipedia. Simply follow the "Edit" link at the top of that page. Be bold in improving articles. When adding facts, please provide references so others may verify them. If you are affiliated with the article subject, please see the conflict of interest guide.

From: http://en.wikipedia.org/wiki/Wikipedia:Contact_us_-_Readers

If you find some incorrect information, there are a few things you can do. First, you can fix it yourself! Anyone can edit Wikipedia. Just hit the "edit" button on the top right of the page, make the correction, and hit "Save page". If you want to learn more about editing, try our help pages.

If you can't or don't want to fix an error, your best approach depends on what kind of problem it is:

• if it's clear vandalism and you can't fix it, please email info-en-v@wikimedia.org and include the address or title of the article and a description of the issue.

(emphasis mine)

If an account is a serial vandal, there are places to report them so that they can be dealt with.

See:

• http://en.wikipedia.org/wiki/Help:Reverting
• http://en.wikipedia.org/wiki/Wikipedia:Vandalism (especially How to respond to vandalism - for beginners)