The singing duo, who dated until he assaulted her on the eve of the Grammy Awards in 2009, posted the new track on file sharing sites, also talking about them on their Twitter pages.
It was rumoured last week that they had been working together on Rihanna's track 'Birthday Cake', which originally appeared on her latest album Talk That Talk.
> Rihanna celebrates 24th birthday in London: Pictures
Brown wrote on his page of the microblogging website earlier today (February 20): "The pub and excitement of this industry /society is only a surface! Really want us as a human race to unite! Bigger than music! (sic)"
Listen to Rihanna and Chris Brown's remix of 'Birthday Cake' below (contains strong language):
Earlier today, the Grammy winner posted a message to Rihanna wishing her a happy birthday. When she asked who wanted some "cake", Brown responded: "Cake, cake cake!" and posted a link to a remix of 'Birthday Cake' on ZShare.
Rihanna wrote to Brown on Twitter: "'Turn up the music' remix," then added: "It's a download OVERLOAD!!! Working on more links for u guys, so err body could have some #CAKE."
Brown was sentenced to 180 days of community labour and five years' probation after pleading guilty to the assault.
He recently told the media that he is "not going anywhere".
> Rihanna starts work on new album
> Chris Brown rides a hover taxi in new 'Turn Up the Music' video
Listen to Rihanna and Chris Brown's version of 'Turn Up the Music' below: