hickory-proto: NSEC3 closest-encloser proof validation enters unbounded loop on cross-zone responses
Date: 2026-05
Affected: rust/hickory-net, rust/hickory-proto
Attack vector: other
Category: vulnerability-disclosure
Severity: High
CWE: CWE-835

The NSEC3 closest-encloser proof validation in `hickory-proto`'s (0.25.0-alpha.3 ... 0.25.2) and `hickory-net`'s (0.26.0-alpha.1 .. 0.26.0) `DnssecDnsHandle` walks from the QNAME up to the SOA owner name, building a list of candidate encloser names. The iterator used assumes the QNAME is a descendant of the SOA owner, terminating only when the current candidate equals the SOA name. When the SOA in a response's authority section is not an ancestor of the QNAME, the loop stalls at the DNS root and never terminates, repeatedly calling `Name::base_name()` and pushing newly allocated `Name` and hashed-name entries into the candidate `Vec`. The bug is reachable by any caller of `DnssecDnsHandle`, including the resolver, recursor, and client, when built with the `dnssec-ring` or `dnssec-aws-lc-rs` feature and configured to perform DNSSEC validation. It is triggered while validating a NoData or NXDomain response whose authority section contains an SOA record from a zone other than an ancestor of the QNAME, on a code path that requires NSEC3 closest-encloser proof. In practice this can be reached through an insecure CNAME chain that crosses zone boundaries into a DNSSEC-signed zone returning NoData, but the minimum condition is just a mismatched SOA owner on a response requiring NSEC3 validation. A `debug_assert_ne!(name, Name::root())` guards the loop body, so debug builds abort with a panic on the first iteration past the root. Release builds compile the assertion out and run the


Mitigations:

Architectural layers (MAESTRO):