A DNSSEC validation vulnerability has been discovered in various DNSSEC validating software. The vulnerability has an assigned number of CVE-2023-50387 and is referred here as the KeyTrap vulnerability. The KeyTrap vulnerability works by using a combination of Keys (also colliding Keys), Signatures and number of RRSETs on a malicious zone. Answers from that zone can force a DNSSEC validator down a very CPU intensive and time costly validation path. It can force Unbound to spend an enormous time (comparative to regular traffic) validating a single specially crafted DNSSEC response while everything else is on hold for that thread. A trivially orchestrated attack could render all threads busy with such responses leading to denial of service. From version 1.19.1 on, Unbound introduces suspension on DNSSEC response validations that seem to require more attempts than Unbound is willing to make per response validation run. Suspension means that Unbound will continue with other work before resuming a suspended validation offering CPU time between validation resumptions to other tasks. There is a backoff timer when suspending which is further influenced by the number of suspends already used and the amount of work currently in Unbound.
*** Bug 924517 has been marked as a duplicate of this bug. ***
1.19.1 is the the tree now
