On 09/15/2015 11:40 AM, Jake Mertel wrote:
C) keep the image firmware file size the same, preventing easy detection of the compromise.
Hmmm...time to automate the downloading and checksumming of the IOS images in my router. Hey, Expect, I'm looking at YOU. Wait a minute...doesn't Cisco have checksums in its file system? This might be even easier than I thought, no TFTP server required... http://www.cisco.com/web/about/security/intelligence/iosimage.html#10 Switch#dir *.bin (Capture the image name) Switch#verify /md5 my.installed.IOS.image.bin The output is a bunch of dots (for a switch) followed by an output line that ends "= xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" with the x's replaced with the MD5 hash. The command is on 2811 routers, too. Maybe far more devices, but I didn't want to take the time to check. You would need to capture the MD5 from a known good image, and watch for changes.