Re: beware: being old sucks

[Dan Mahoney via NANOG <nanog () lists nanog org>]

Randy,

Something else I recently discovered that relates to this issue: 

I think there’s a serious flaw in the way ssh key hashes are done on IOS.  I’ve been in touch with Cisco CSIRT about 
it, and they’ve approved publication, but in short, if you’re using pubkey auth to a cisco device, you might want to 
rethink it.  

Short version: Unlike normal pubkeys, IOS only stores an md5 hash of your key to auth against, and you can thus use any 
key that matches that hash.  Which an attacker now has.

https://gushi.medium.com/what-i-learned-from-configuring-ssh-pubkey-auth-on-cisco-ios-cbeb1e5b3b77

(should not be paywalled, email me privately if it is)

> On Aug 30, 2025, at 11:30, Randy Bush via NANOG <nanog () lists nanog org> wrote:
>
> a fellow nanogger wrote:
>
> > I've only *just* gotten to the note from a week or more ago.
> >
> > >    + tftp-server nvram:startup-config          <<<<<<======
> > >      snmp-server community foo 98
> > >      snmp-server trap-source Vlan1
> > >      snmp-server location Ashburn VA US
> >
> > I, too, got this from a RANCID setup I built a long time ago.
> >
> > > and here is the talos report, thanks joe
> > >
> > >   https://blog.talosintelligence.com/static-tundra/
> > >
> > > set `no vstack` in config.  no, that is not the default.
> >
> > I'd told the owner that I didn't think he had control of his gear
> > anymore, but this helped me to convince him to put a new switch in.
>
> moving this to nanog because i did not elaborate on a critical point.
>
> when you get this, presume the config of this trivial ancient devic has
> been snatched.  did the device have any burned in users, a la
>
>     username foo privilege 15 password 7 bar
>
> and that uid/pass is used on other, presumably more modern, devices,
> you need to change the passwords everywhere.
>
> same for other credentials, snmp, bgpmd5, ...
>
> randy
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