full-disclosure - Re: owning ubuntu apt-key net-update (maybe apt-get update related)

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Date: Thu, 22 Sep 2011 15:03:08 +0300
From: Georgi Guninski <guninski@...inski.com>
To: full-disclosure@...ts.grok.org.uk
Subject: Re: owning ubuntu apt-key net-update (maybe
 apt-get update related)

# grep -rniI 'apt-key' /etc 2>/dev/null 
/etc/cron.daily/apt:444:    if eval apt-key net-update $XSTDERR; then
/etc/cron.daily/apt:445:        debug_echo "apt-key net-update (success)"
/etc/cron.daily/apt:447:        debug_echo "apt-key net-update (failure)"

i suppose this effectively breaks vanilla "apt-get update" after cron is helped by MITM.

the certs were verified to work after installed by apt-key net-update.

-- 
joro

On Thu, Sep 22, 2011 at 12:07:08PM +0300, Georgi Guninski wrote:
> owning ubuntu apt-key net-update (maybe apt-get update related)
> 
> in ubuntu 10.04 in /usr/bin/apt-key in add_keys_with_verify_against_master_keyring()
> 
> if $GPG_CMD --keyring $ADD_KEYRING --list-sigs --with-colons $add_key | grep ^sig | cut -d: -f5 | grep -q $master_key; then
> 		$GPG_CMD --quiet --batch --keyring $ADD_KEYRING --export $add_key | $GPG --import
> 		ADDED=1
> 
> 
> to my knowledge --list-sigs doesn't do crypto verification, just looks for well formedness.
> 
> it is trivial to generate a gpg key with key ID == $master_key:
> set gpg version to 3, set the lowest 64 bits of the RSA $n$ to the key ID, generate random high bits until one can trial factor $n$ (numerology is on your side), this is it.
> 
> to reproduce:
> attached is ubuntu-archive-keyring.gpg.
> put it on http://A/ubuntu-archive-keyring.gpg
> make a copy of apt-key and set:
> ARCHIVE_KEYRING_URI=http://A/ubuntu-archive-keyring.gpg
> ^ this emulates MITM.
> do |./apt-key-new net-update| and check for new keys with |apt-key list|
> 
> this might or might not be related with |apt-get update|.
> 
> 10x.
> 
> -- 
> joro
> 
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Charter: http://lists.grok.org.uk/full-disclosure-charter.html
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