RFC 6840, "Clarifications and Implementation Notes for DNS Security (DNSSEC)", February 2013

Note: This RFC has been updated by RFC 8749

Errata ID: 8038
Status: Reported
Type: Technical
Publication Format(s) : TEXT
Reported By: Elias Heftrig
Date Reported: 2024-07-18

Section 4.2. says:

   When validating a response to QTYPE=*, all received RRsets that match
   QNAME and QCLASS MUST be validated.  If any of those RRsets fail
   validation, the answer is considered Bogus.

It should say:

   When validating a response to QTYPE=*, all received RRsets that match
   QNAME and QCLASS SHOULD be validated.  If any of those RRsets fail
   validation, the answer is considered Bogus.

Notes:

The original text requires validators to invest an unreasonable amount of work to validate the signatures over the RRsets in case there are many such RRsets. The issue was exploited in the construction of CPU resource exhaustion attacks (CVE-2023-50387). For more details see our publication with ACM CCS'24 on the KeyTrap denial of service vulnerabilities.

Note that further elaboration is required to clarify the implications of not following the recommendation. We suggest to also update the second sentence along the lines of:
> If any of those RRsets fail validation or the response contains more such RRsets than the validator is willing to process, the answer is considered Bogus.

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