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

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Message-ID: <20110922090708.GA2117@sivokote.iziade.m$>
Date: Thu, 22 Sep 2011 12:07:08 +0300
From: Georgi Guninski <guninski@...inski.com>
To: full-disclosure@...ts.grok.org.uk
Subject: owning ubuntu apt-key net-update (maybe apt-get
	update related)

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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