Paul Singer's Elliott Management getting activist on Juniper, Riverbed

Paul Singer, founder and president of Elliott Management Corp.
Jacob Kepler | Bloomberg | Getty Images

Paul Singer's Elliott Management is flexing its activist muscles this week and has plans for much more in 2014.

A portfolio manager at the $23 billion hedge fund firm, Jesse Cohn, is aggressively pushing for changes at technology companies Riverbed Technology and Juniper Networks in a series of public letters meant to prod action—and higher stock prices.

It seems to be to be working.

Juniper jumped from about $22 a share Friday to more than $25 as of Tuesday following a filing from Cohn calling for "cost realignment, capital return to shareholders, and the optimization of Juniper's product portfolio." Elliott, which owns 6.2 percent of Juniper, believes the plan will cause the stock to rise as high as $35 or $40 per share.