Is there any method that administrators should use to verify IOS image integrity and spot backdoors?
Have the image on known-to-be-good storage and compare the SHA-1 hashes with the image you are loading to the router via network. On your slides for BlackHat Federal 2003, I read that someone told you that he was able to place a backdoor on IOS. Can you share any info about that? It’s actually pretty easy, as I have presented at Defcon 11 in the runtime image patching code. Of course you can do the same thing with an image, recalculate and replace the already mentioned checksums and give it to someone. That has been done in the past and since few people have valid CCO accounts to download their images directly from Cisco, it’s easy to convince someone to install your backdoored image. Cisco should make all IOS images freely available. This would increase their hardware sales and improve security, since people would no longer need to actually pay for SSH support. Before the recent CCO compromise, everyone used someone else’s account. But now, most people don’t have an account to use any
