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Kaspersky SSL Interception Differentiation

Kaspersky SSL Interception Differentiation
Posted Jan 3, 2017
Authored by Tavis Ormandy, Google Security Research

In order to inspect encrypted data streams using SSL/TLS, Kaspersky installs a WFP driver to intercept all outgoing HTTPS connections. They effectively proxy SSL connections, inserting their own certificate as a trusted authority in the system store and then replace all leaf certificates on-the-fly. This is why if you examine a certificate when using Kaspersky Antivirus, the issuer appears to be "Kaspersky Anti-Virus Personal Root". Kaspersky's certificate interception has previously resulted in serious vulnerabilities, but quick review finds many simple problems still exist. For example, the way leaf certificates are cached uses an extremely naive fingerprinting technique. Kaspersky cache recently generated certificates in memory in case the user agent initiates another connection. In order to do this, Kaspersky fetches the certificate chain and then checks if it's already generated a matching leaf certificate in the cache. If it has, it just grabs the existing certificate and private key and then reuses it for the new connection. The cache is a binary tree, and as new leaf certificates and keys are generated, they're inserted using the first 32 bits of MD5(serialNumber||issuer) as the key. If a match is found for a key, they just pull the previously generated certificate and key out of the binary tree and start using it to relay data to the user-agent. You don't have to be a cryptographer to understand a 32bit key is not enough to prevent brute-forcing a collision in seconds. In fact, producing a collision with any other certificate is trivial.

tags | exploit, web, root, vulnerability, virus
MD5 | 2546662d9e3ac6122c369f4d26198f24

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