hickory-resolver: Unbounded TC-retry loop in NameServerPool::try_send (resource-exhaustion DoS)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

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

Published by the source

5 Oct 2026, 22:55 UTC

Last modified by the source

5 Oct 2026, 23:15 UTC

Source last checked

26 Oct 2026, 15:43 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-6w6g-hm98-mhgm

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-6w6g-hm98-mhgm

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# Patch Next advisory brief: GHSA-6w6g-hm98-mhgm

Advisory: hickory-resolver: Unbounded TC-retry loop in `NameServerPool::try_send` (resource-exhaustion DoS)
IDs: GHSA-6w6g-hm98-mhgm
Record: https://patchnext.com/advisories/ghsa-6w6g-hm98-mhgm (revision 3, source checked 26 Oct 2026, 15:43 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: hickory-resolver 0.26.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io hickory-resolver: affected >= 0.26.0-beta.1, < 0.26.2; fixed in 0.26.2

## Suggested inspection (read-only)
- crates.io hickory-resolver: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on hickory-resolver.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-6w6g-hm98-mhgm (OSV record GHSA-6w6g-hm98-mhgm lists affected ranges: crates.io hickory-resolver >=0.26.0-beta.1 <0.26.2 (fixed))
- Verified: https://github.com/advisories/GHSA-6w6g-hm98-mhgm (GitHub-reviewed advisory GHSA-6w6g-hm98-mhgm lists affected ranges: crates.io hickory-resolver >=0.26.0-beta.1 <0.26.2)

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