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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: 0.22s | 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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Bu9818 ◴[21 Oct 23 01:59 UTC] No.37963431[source]▶
>affected 100% of the connections to XMPP STARTTLS port 5222 (not 5223)

Why did they only target the STARTTLS port? On a related note, I would never use the STARTTLS port (opportunistic encryption) if I knew that the server had a regular TLS port...

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1. upofadown ◴[21 Oct 23 11:53 UTC] No.37966043[source]▶
>I would never use the STARTTLS port (opportunistic encryption) if I knew that the server had a regular TLS port...

That is what XMPP clients tend to do...

These days XMPP servers tend to default to requiring TLS on both 5222 and 5223 (Let's Encrypt has changed everything). Prosody does this for example. It doesn't even support port 5223 by default anymore. Port 5223 was never an official port assignment.

So it is very possible that the MiTM was only done on port 5222 because that was the only port that clients were using.