The products are Cisco's Web Security Virtual Appliance, Email Security Virtual Appliance and Security Management Virtual Appliance, it said in an advisory. Versions downloaded before Thursday are vulnerable.
Cisco said it "is not aware of any public announcements or malicious use of the vulnerabilities that are described in this advisory."
The three products all shipped with preinstalled encryption keys for SSH (Secure Shell), which is used to remotely log into machines. It's considered a bad security practice to ship products that all have the same private keys.
If attackers obtained the private keys, it would be possible to decrypt traffic after collecting it during a man-in-the-middle attack. It would also be possible to impersonate one of the appliances or alter traffic, Cisco warned.
The patch deletes the preinstalled SSH keys and provides instructions for how customers can completely fix the problem. Cisco wrote that the patch is not required for physical hardware appliances or for virtual appliance downloads or upgrades after Thursday.
The fix is named "cisco-sa-20150625-ironport SSH Keys Vulnerability Fix" in a list of product upgrades. It must be manually installed from a command line interface, it said.
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