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Bug#618863: /usr/bin/ssh: insecurely verifies host key with VerifyHostKeyDNS option



On Fri, Mar 18, 2011 at 07:41:36PM -0700, Rob Leslie wrote:
> When the VerifyHostKeyDNS option is used, ssh attempts to verify unknown
> remote host keys by looking up SSHFP records in DNS. It relies on the AD
> (Authentic Data) flag in the response to determine whether the fingerprint
> it receives has been cryptographically verified by the resolver (i.e. with
> DNSSEC) and if so, may rely on the matching host key with no further
> verification.

Interestingly the default changed from "yes" to "no" at some point.

openssh (1:5.4p1-2) unstable; urgency=low

  * Borrow patch from Fedora to add DNSSEC support: if glibc 2.11 is
    installed, the host key is published in an SSHFP RR secured with DNSSEC,
    and VerifyHostKeyDNS=yes, then ssh will no longer prompt for host key
    verification (closes: #572049).
[…]

 -- Colin Watson <cjwatson@debian.org>  Sat, 10 Apr 2010 01:08:59 +0100

And I just had to flip it on manually. The manual page also says that
it's off byd efault.

The problem with authoriative servers not setting AD is also something I
personally experienced and which is quite annoying. But then I agree
that authoriative and recursor should be split nowadays, although it's a
bit hard to do in a home network environment.

Kind regards
Philipp Kern

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