NetNanny installs a Man-in-the-Middle (MITM) proxy as well as a new trusted root CA certificate. The certificate used by NetNanny is shared among all installations of NetNanny. Furthermore, the private key used to generate the certificate is also shared and may be obtained in plaintext directly from the software. An attacker may use this shared private key to generate new certificates that would be signed by and therefore trusted by NetNanny. An affected user would not be alerted to a false malicious HTTPS website as NetNanny would trust the spoofed certificate. NetNanny has provided more information on this issue on their FAQ.

We have confirmed that NetNanny version 7.2.4.2 is affected. Other versions may also be affected.

For more information on the impact of this issue on SSL inspection, please see Will Dormann's CERT/CC blog post on SSL Inspection.

An attacker can spoof HTTPS sites and intercept HTTPS traffic without triggering browser certificate warnings in affected systems.

Update NetNanny

ContentWatch has released NetNanny for Windows version 7.2.5.1 which addresses these issues. Affected users should update as soon as possible.

Disable SSL filtering and remove the certificate

Affected users can disable SSL filtering using the interface, and manually delete the certificate from the operating system's certificate store. This prevents the issue described above while leaving most other features of NetNanny intact.

Uninstall NetNanny

Uninstalling NetNanny removes the root CA certificate from the operating system's certificate store.