Well, It would be pointless to do, If the flash version and the running executable already replaced that function to return the right MD5 as from the CCO repository... But yes, scheduling the downloading the firmware and doing a SHA512 from your known good source (aka the Cisco one pre-deployement), would be the method I would use. ( We're doing it quarterly in some cases ) ----- Alain Hebert ahebert@pubnix.net PubNIX Inc. 50 boul. St-Charles P.O. Box 26770 Beaconsfield, Quebec H9W 6G7 Tel: 514-990-5911 http://www.pubnix.net Fax: 514-990-9443 On 09/15/15 16:46, Stephen Satchell wrote:
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.