dnsdist: Add security advisory 2024-03 for DNSdist

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+PowerDNS Security Advisory 2024-03: Transfer requests received over DoH can lead to a denial of service in DNSdist
+==================================================================================================================
+
+- CVE: CVE-2024-25581
+- Date: May 13th 2024
+- Affects: PowerDNS DNSdist 1.9.0, 1.9.1, 1.9.2 and 1.9.3, earlier versions are not affected
+- Not affected: PowerDNS DNSdist 1.9.4
+- Severity: High (only in specific configurations, see below)
+- Impact: Denial of service
+- Exploit: This problem can be triggered by a remote, unauthenticated attacker sending a DNS query
+- Risk of system compromise: None
+- Solution: Upgrade to patched version or apply the workaround described below
+
+When incoming DNS over HTTPS support is enabled using the nghttp2 provider, and queries are routed to a tcp-only or
+DNS over TLS backend, an attacker can trigger an assertion failure in DNSdist by sending a request for a zone transfer
+(AXFR or IXFR) over DNS over HTTPS, causing the process to stop and thus leading to a Denial of Service.
+DNS over HTTPS is not enabled by default, and backends are using plain DNS (Do53) by default.
+
+`CVSS Score: 7.5 <https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H&version=3.1>`__, only for configurations where incoming DoH is enabled and a TCP-only/DoT backend is enabled.
+
+Two workarounds are available:
+- refuse incoming XFR requests via a DNSdist rule: ``addAction(OrRule({QTypeRule(DNSQType.AXFR), QTypeRule(DNSQType.IXFR)}), RCodeAction(DNSRCode.REFUSED))``
+- switch to the legacy h2o provider by setting ``library='h2o'`` in the ``addDOHLocal`` directive
+
+For those unable to upgrade to a new version, a minimal patch is `available for 1.9.3 <https://downloads.powerdns.com/patches/2024-03>`__
+
+We would like to thank Daniel Stirnimann from Switch for finding and subsequently reporting this issue.