# RUSTSEC-2026-0106: Record cache accepts AUTHORITY section NS from sibling zone via parent-pool zone-context elevation


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 22 Apr 2026

## What is RUSTSEC-2026-0106?

RUSTSEC-2026-0106 is a vulnerability in hickory-recursor, published on 22 Apr 2026. 

### Official description

The Hickory DNS project's experimental `hickory-recursor` crate's record cache
(`DnsLru`) stores records from DNS responses keyed by each record's own (name,
type), not by the query that triggered the response. `cache_response()` in
`crates/recursor/src/lib.rs` chains `ANSWER`, `AUTHORITY`, and `ADDITIONAL`
sections into one record iterator before insertion. The bailiwick filter it
applies uses the zone context of the NS pool that serviced the lookup, not the
zone being queried.

This creates a cross-zone poisoning path. When Hickory builds the NS pool for
`attacker.poc.` it uses the parent `poc.` `NS` pool (`ns.zone() = "poc."`). If
the `poc.` nameserver under the attacker's control includes in its response's
`AUTHORITY` section a record for a sibling zone like `victim.poc. NS
ns.evil.poc.`, the bailiwick check `is_subzone("poc.", "victim.poc.")` passes
(`victim.poc.` is a subdomain of `poc.`). The record is stored under
`(victim.poc., NS)` in the shared cache.

Subsequently, any client querying a name in `victim.poc`. causes Hickory to
build its NS pool from the poisoned cache entry, routing queries to the
attacker's nameserver (`ns.evil.poc.`) rather than to the legitimate nameserver
for `victim.poc.`. The legitimate `NS` for that zone receives zero queries.

This issue is fixed in `hickory-resolver` 0.26.0 with the `recursor` feature
through an architectural change to response-level caching: responses are stored
keyed by the originating query `(name, type)`. A response to `(attacker.poc.
NS)` is stored only under that key and cannot affect the `(victim.poc., NS)`
cache entry.

We believe this issue has been present in all published versions of the
experimental `hickory-recursor` crate, which has now been folded into the
`hickory-resolver` crate under the non-default `recursor` feature flag. The
`hickory-recursor` crate will not receive any updates going forward and all
users should migrate to `hickory-resolver` with the `recursor` feature.

## Which versions are affected by RUSTSEC-2026-0106?

1 open source package ship an affected version, including hickory-recursor.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hickory-recursor` | crates.io | From 0.0.0-0 | None |

## How do I fix RUSTSEC-2026-0106?

No fix has been published for RUSTSEC-2026-0106 yet. Limit exposure of the affected software until one is available.

## Is RUSTSEC-2026-0106 being exploited?

There is no known exploitation of RUSTSEC-2026-0106 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0106 and fix it if it is affected.

What it is: RUSTSEC-2026-0106 is a vulnerability in hickory-recursor, published on 22 Apr 2026. 
Exploitation: There is no known exploitation of RUSTSEC-2026-0106 in the wild and no public exploit code.

Affected packages and fixed versions:
- hickory-recursor (crates.io): affected from 0.0.0-0; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/RUSTSEC-2026-0106/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0106/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0106

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0106/
Summaries are generated and may contain mistakes; the official description above is the record.