The investment follows on from an agreement signed between the two companies last month for Juniper to resell and support Corero's SmartWall cybersecurity software products and services.
Corero said the cash would give it more headroom to meet its objective of becoming cash generating and EBITDA profitable during 2019. Juniper provides the routing infrastructure for some of the world's largest IP networks and cloud data centres.
The California-based company will pay a subscription price of 8.9p each for its shares, which will amount to a 4.23% stake in Corero.
Ashley Stephenson, Corero’s chief executive, said the investment underlined its belief SmartWall products are a critical component in securing IT networks from DDoS attacks.