Cisco has warned its corporate customers that three router operating system vulnerabilities have been found, which could allow a hacker to commit denial-of-service attacks against websites.

The internet network company released an advisory on Wednesday detailing the three flaws, which affect its Internetwork Operating System Software (IOS), and how a malicious user could execute code on the impaired products.  Customers are advised to upgrade to a fixed version of IOS, the firm said.

“Cisco is aware of multiple vulnerabilities that may impact IOS and IOS XR devices and has published three security advisories,” a spokesperson said in a statement.  “Cisco is also not aware of any current exploitation of these vulnerabilities.”

The Californian company has released free software available to users to address the flaws, according to the spokesperson.