# GHSA-6w6g-hm98-mhgm: hickory-resolver: Unbounded TC-retry loop in `NameServerPool::try_send` (resource-exhaustion DoS)

> A malicious DNS server can cause a resource-exhaustion denial of service in the hickory-resolver library by triggering an unbounded retry loop on truncated responses.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 5 Oct 2026

## What is GHSA-6w6g-hm98-mhgm?

GHSA-6w6g-hm98-mhgm is a denial of service vulnerability in hickory-resolver, published on 5 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

When the `hickory-resolver` name server pool implementation receives an upstream response with the TC (truncated) header bit set, it re-queues the request to the same nameserver to retry with UDP transport disabled. However, the retry arm never inspects the transport that just answered and carries no iteration counter. An authoritative server that sets `TC=1` on **every** available transport  keeps the resolver spinning on one persistent TCP connection until the 5s per-request wall-clock deadline expires.

### Reporter

Qifan Zhang, Palo Alto Networks

## Which versions are affected by GHSA-6w6g-hm98-mhgm?

2 open source packages ship an affected version, including hickory-resolver.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hickory-resolver` | crates.io | From 0.26.0-beta.1 | 0.26.2 |
| `hickory-resolver` | crates.io | From 0.26.0-beta.1 | 0.26.2 |

## How do I fix GHSA-6w6g-hm98-mhgm?

Upgrade hickory-resolver to 0.26.2 or later.

## Is GHSA-6w6g-hm98-mhgm being exploited?

There is no known exploitation of GHSA-6w6g-hm98-mhgm in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-6w6g-hm98-mhgm and fix it if it is affected.

What it is: GHSA-6w6g-hm98-mhgm is a denial of service vulnerability in hickory-resolver, published on 5 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-6w6g-hm98-mhgm in the wild and no public exploit code.

Affected packages and fixed versions:
- hickory-resolver (crates.io): affected from 0.26.0-beta.1; fixed in 0.26.2
- hickory-resolver (crates.io): affected from 0.26.0-beta.1; fixed in 0.26.2

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/GHSA-6w6g-hm98-mhgm/ (Markdown: https://insights.sbomify.com/GHSA-6w6g-hm98-mhgm/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-6w6g-hm98-mhgm

---
From sbomify Insights: https://insights.sbomify.com/GHSA-6w6g-hm98-mhgm/
Summaries are generated and may contain mistakes; the official description above is the record.