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Mitigating the Hetzner/Linode XMPP.ru MitM interception incident

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341 points hlandau | 1 comments | 20 Oct 23 20:31 UTC | HN request time: 0s | source
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LeoPanthera ◴[20 Oct 23 22:54 UTC] No.37962383[source]▶
The summary of the attack from https://notes.valdikss.org.ru/jabber.ru-mitm/ is very interesting:

* The attacker managed to issue multiple SSL/TLS certificates via Let’s Encrypt for jabber.ru and xmpp.ru domains since 18 Apr 2023

* The Man-in-the-Middle attack for jabber.ru/xmpp.ru client XMPP traffic decryption confirmed to be in place since at least 21 July 2023 for up to 19 Oct 2023, possibly (not confirmed) since 18 Apr 2023, affected 100% of the connections to XMPP STARTTLS port 5222 (not 5223)

* The attacker failed to reissue TLS certificate and MiTM proxy started to serve expired certificate on port 5222 for jabber.ru domain (Hetzner)

* The MiTM attack stopped shortly after we begun our investigation and network tests on 18 Oct 2023, along with tickets to Hetzner and Linode support team, however passive wiretapping (additional routing hop) is still in place at least on a single Linode server

* Neither servers appear to be hacked

* Both Hetzner and Linode network appear to be reconfigured specifically for this kind of attack for the XMPP service IP addresses

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Neither that page, nor the page linked from here, mention certificate pinning, maybe because XMPP doesn't support it (I don't know), but if it did, wouldn't that have prevented this kind of attack?

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simpaticoder ◴[21 Oct 23 01:18 UTC] No.37963258[source]▶
>The attacker managed to issue multiple SSL/TLS certificates via Let’s Encrypt

This implies that the attacker was able to validate domain ownership of jabber.ru and xmpp.ru by either a) being able to respond to the ACME protocol on domain(s) hosted http OR b) being able to write to a DNS TXT file for the domain(s). This implies that the victim already lost control of their process server and/or their nameserver.

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tetromino_ ◴[21 Oct 23 01:35 UTC] No.37963315[source]▶
No. Most probably it merely implies someone upstream of them (presumably their hosting provider under compulsion from German law enforcement) intercepted and spoofed their unencrypted, unauthenticated ACME HTTP traffic.

Same can happen to you.

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simpaticoder ◴[21 Oct 23 02:54 UTC] No.37963692[source]▶
Okay, but the part I don't understand is why do it this way? If the hosting provider is a threat, they don't need new certs. They can just read your private keys off your disk and MITM with that.
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1. fulafel ◴[21 Oct 23 03:34 UTC] No.37963855[source]▶
Here's a good example why trust is not binary ("you either trust Hetzner or don't"). Quite possibly wiretapping law doesn't require them to facilitate the server breakin.