14 DAY TRIAL // PrivDog, the free browsing privacy protection tool endorsed Comodo, has been found to offer an insecure implementation of the way it uses its own root certificate to validate the certificates from HTTPS websites.
The free utility is designed to replace the potentially malicious advertisements in a site accessed by the user with other banners that come from a “trusted source.”
It does so by installing its root certificate on the client machine and placing itself between the client and the server (man-in-the-middle) to intercept traffic and by re-signing the certificates presented by websites offering a secure connection.
Self-signed certificates trusted implicitly
Security researcher Johannes Böck has analyzed the actions taken by the free utility to achieve its task and says that PrivDog intercepts and replaces any certificate, regardless if it is verified by a higher authority in the chain of trust or not.
Any owner of a website can self-sign a certificate to create an encrypted connection with the client. As per the chain of trust model, it has to be validated by a root certificate, which belongs to a trusted certificate authority (CA) and is included in an accredited repository such as the one provided by Microsoft in Windows or the one included by Mozilla in Firefox and Thunderbird.
If a certificate not validated by a CA is used, the browser issues a warning informing the user that it could not verify its authenticity. Comodo is a CA, though, with a root certificate in Windows that offers server authentication.
Oddities discovered
“PrivDog will intercept every certificate and replace it with one signed by its root key. And that means also certificates that weren't valid in the first place. It will turn your Browser into one that just accepts every HTTPS certificate out there, whether it's been signed by a certificate authority or not,” Böck says in a blog post published on Monday.
Because of this, Böck alleges that the model adopted by PrivDog may create a greater risk to the user than the one posed by Superfish, which used a single certificate with the same RSA key on all machines it was installed on.
The researcher also found other things he deemed “completely weird.” One of them refers to adding into the root certificate in Windows another self-signed certificate with a 512 RSA key. The second one is that all other certificates are replaced by 1024-bit RSA certificates that are validated by a PrivDog CA that is generated locally.
[UPDATE]:A statement was issued on Monday by PrivDog, informing that an update was released with a fix for the issue.
According to the PrivDog team, the problem could potentially affect about 64,000 users worldwide and was limited only to the standalone release. The versions bundled in other Comodo products did not include the flaw.
The company downplayed the risk posed by the flaw and marked it with a “low” threat level, saying that the danger occurs “if a user visits a site that actually has a self-signed certificate.”
