Hickory DNS hickory-proto 0.25.0-alpha.3 through 0.25.2 and hickory-net before 0.26.1 contain an unbounded loop vulnerability in DnssecDnsHandle NSEC3 closest-encloser proof validation when the SOA owner is not an ancestor of the QNAME. Upstream attackers can return NoData or NXDomain responses with a cross-zone SOA record to panic debug builds or exhaust memory in release builds.

Hickory DNS hickory-proto 0.25.0-alpha.3 through 0.25.2 and hickory-net before 0.26.1 contain an unbounded loop vulnerability in DnssecDnsHandle NSEC3 closest-encloser proof validation when the SOA owner is not an ancestor of the QNAME. Upstream attackers can return NoData or NXDomain responses with a cross-zone SOA record to panic debug builds or exhaust memory in release builds.

Affected: crates.io: hickory-proto

The NSEC3 closest-encloser proof validation in `hickory-proto`'s `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 loop unbounded, allocating until the process exhausts available memory (…

Affected: Ubuntu:24.04:LTS: rust-hickory-proto, Ubuntu:26.10: rust-hickory-proto, Ubuntu:26.04:LTS: rust-hickory-proto

Hickory DNS hickory-proto 0.25.0-alpha.3 through 0.25.2 and hickory-net before 0.26.1 contain an unbounded loop vulnerability in DnssecDnsHandle NSEC3 closest-encloser proof validation when the SOA owner is not an ancestor of the QNAME. Upstream attackers can return NoData or NXDomain responses with a cross-zone SOA record to panic debug builds or exhaust memory in release builds.