Kaspersky fixed a certificate validation error in the software which affected 400 million users.
It was discovered by Google's stubborn bug-hunter Tavis Ormandy. The flaw lies in how the company's antivirus inspects encrypted traffic.
Since it decrypts traffic before inspection, Kaspersky presents its certificates as a trusted authority. If a user opens Google in their browser, for example, the certificate will appear to come from Kaspersky Anti-Virus Personal Root.
The problem that Ormandy found was that the internal certificates were incredibly weak.
“As new certificates and keys are generated, they are entered using the first 32 bits of 3MD5(serialNumber||issuer) as a key... You don't need to be a cryptographer to understand that a 32-bit key is not enough to prevent attacks brute-force", says the researcher.
For the bug report Ormandy provided a PoC conflictof certificates between Hacker News and manchesterct.gov:
“If you use Kaspersky Antivirus on Manchester, and you're wondering why Hacker News doesn't work sometimes, it's because a critical vulnerability disabled SSL certificate validation for 400 million Kaspersky users.”
Kaspersky reportedly corrected the 28 December error.
Kaspersky: SSL interception differentiates certificates with a 32bit hash
