[PL-133007] implement the D(HE)at Attack mitigation

[PhilTaken]

mitigate CVE-2024-41996

Since restricting encryption curves might impact compatibility with various clients, this was made an option for now with the default being on so that it can be turned off selectively.

@flyingcircusio/release-managers

Release process

• Created changelog entry using ./changelog.sh

PR release workflow (internal)

• PR has internal ticket
• internal issue ID (PL-…) part of branch name
• internal issue ID mentioned in PR description text
• ticket is on Platform agile board
• ticket state set to Pull request ready
• if ticket is more urgent than within the next few days, directly contact a member of the Platform team

Design notes

• Provide a feature toggle if the change might need to be adjusted/reverted quickly depending on context. Consider whether the default should be on or off. Example: rate limiting.
• All customer-facing features and (NixOS) options need to be discoverable from documentation. Add or update relevant documentation such that hosted and guided customers can understand it as well.

Security implications

• Security requirements defined? (WHERE)
  • mitigates CVE-2024-41996
• Security requirements tested? (EVIDENCE)

without the patch

λ ❱ dheat --protocol [ ... ]
2024-11-12T11:01:34+0100 Server offers protocol version TLS 1.2
2024-11-12T11:01:34+0100 Server offers protocol version TLS 1.3 supported
### Software

    * Version: 0.4.3

### Arguments

    * Thread num: 1
    * Protocol: TLS 1.3
    * Address: [ ... ]

### Service

    * IP: [ ... ]
    * Port: 443
    * Key size: 8192
    * Algorithm: TLS_AES_128_GCM_SHA256
^C⏎

with the patch

λ ❱ dheat --protocol tls [ ... ]
2024-11-12T10:59:37+0100 Server offers protocol version TLS 1.2
2024-11-12T10:59:37+0100 Server offers protocol version TLS 1.3 supported
Diffie-Hellman ephemeral (DHE) key exchange (with the given key size) not supported by the server; uri="[ ... ]", protocol="tls"

see also the internal ticket for a more detailed writeup

[osnyx]

Please include which exact curve is disabled, such that customers can determine whether they're affected or not from changelog information alone.

[ctheune]

Looks good in general, but I'd like to see a changelog entry that's more suitable for people not as deep into the context as we are. ;)

[PhilTaken]

I hope this wording makes more sense to non-technical people. Cryptography has a tendency of being quite tough to explain IME

[osnyx]

rebased onto fc-24.05-dev, hoping this fixes the gitlab test.

Suggested changes have been implemented.