xzbot – A Strategic Approach To Counter CVE-2024-3094 Through Honeypots And ED448 Patches

We delve into the intricacies of xzbot, a tool designed to combat the CVE-2024-3094 vulnerability.

By employing a combination of honeypots, custom ED448 patches, and detailed backdoor analysis, we provide a robust framework for detecting and mitigating exploit attempts.

This guide outlines the steps to utilize xzbot effectively, ensuring your systems are safeguarded against potential breaches.

Exploration of the xz backdoor (CVE-2024-3094). Includes the following:

• honeypot: fake vulnerable server to detect exploit attempts
• ed448 patch: patch liblzma.so to use our own ED448 public key
• backdoor format: format of the backdoor payload
• backdoor demo: cli to trigger the RCE assuming knowledge of the ED448 private key

Honeypot

See openssh.patch for a simple patch to openssh that logs any connection attempt with a public key N matching the backdoor format.

$ git clone https://github.com/openssh/openssh-portable
$ patch -p1 < ~/path/to/openssh.patch
$ autoreconf
$ ./configure
$ make

Any connection attempt will appear as follows in sshd logs:

$ journalctl -u ssh-xzbot --since='1d ago' | grep xzbot:
Mar 30 00:00:00 honeypot sshd-xzbot[1234]: xzbot: magic 1 [preauth]
Mar 30 00:00:00 honeypot sshd-xzbot[1234]: xzbot: 010000000100000000000000000000005725B22ED2...

ED448 Patch

The backdoor uses a hardcoded ED448 public key for signature validation and decrypting the payload. If we replace this key with our own, we can trigger the backdoor.

The attacker’s ED448 key is:

0a 31 fd 3b 2f 1f c6 92 92 68 32 52 c8 c1 ac 28
34 d1 f2 c9 75 c4 76 5e b1 f6 88 58 88 93 3e 48
10 0c b0 6c 3a be 14 ee 89 55 d2 45 00 c7 7f 6e
20 d3 2c 60 2b 2c 6d 31 00

We will replace this key with our own (generated with seed=0):

5b 3a fe 03 87 8a 49 b2 82 32 d4 f1 a4 42 ae bd
e1 09 f8 07 ac ef 7d fd 9a 7f 65 b9 62 fe 52 d6
54 73 12 ca ce cf f0 43 37 50 8f 9d 25 29 a8 f1
66 91 69 b2 1c 32 c4 80 00

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