The uTorrent client was recently updated to fix a null pointer dereference (CVE-2020-8437), discovered by [whtaguy]. Triggering the dereference simply crashes the client — so far an actual RCE hasn’t been found. Given the nature of the null pointer dereference, it’s possible this bug is limited to denial of service. That’s extremely good, because the flaw is extremely easy to target.

BitTorrent is a clever protocol. It’s still used to distribute large files, like Linux ISOs. The concept is simple: Split a large file into small chunks. Send the chunks to a client one at a time. As each chunk is received, the client sends a copy of that chunk to the next client. As a result of this peer-to-peer (p2p) arrangement, the bandwidth available to the server is greatly multiplied. As with all other p2p arrangements, the sticking point is how to make those connections between peers, particularly when most of the world’s desktops are behind NAT routers. In practice, for two peers to share data, at least one of them has to have a port opened or forwarded to the client. This is often accomplished through Universal Plug-n-Play (UPnP) or the NAT Port Mapping Protocol (NAT-PMP). The idea of both protocols are the same; a client on an internal device can request a temporary port forward without manual intervention. Whether it’s a good idea to allow automatic port forwards is another issue for another day. Continue reading “This Week In Security: UTorrent Vulnerable, Crowd-Sourcing Your Fail2Ban, And Cryptographers At Casinos” →