# CVE-2026-42387: PowerDNS Recursor denial of service in ZoneToCache

Source: https://junglewise.ai/threats/cve-2026-42387-powerdns-recursor-denial-of-service-in-zonetocache  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-25. Updated: 2026-06-25  
License: CC BY 4.0 with a link back

CVE-2026-42387 · Severity: medium · CVSS 5.9 · Published 2026-06-25

A vulnerability in the PowerDNS Recursor, a service used to translate human-readable domain names into IP addresses, could allow a malicious server to crash the system. By sending a specially crafted data zone, an attacker can trigger a service failure, leading to a denial of service for users relying on that DNS server. This impact is limited to service availability and does not involve data theft or unauthorized access.

Technologies: [Powerdns Recursor](https://junglewise.ai/threats/technologies/recursor). Vendors: [Powerdns](https://junglewise.ai/threats/vendors/powerdns).

## Quick answers

**Is CVE-2026-42387 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42387 being exploited in the wild.

**How severe is CVE-2026-42387?** Medium severity, with a CVSS score of 5.9, published 25 June 2026.

**Which products and versions are affected?** Powerdns Recursor 5.2.0 to 5.2.10, 5.3.0 to 5.3.7, 5.4.0 to 5.4.2.

**Is there a fix for CVE-2026-42387?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-42387 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-42387?** Check whether you run Powerdns Recursor at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A denial of service vulnerability exists in PowerDNS Recursor's ZoneToCache function due to insufficient input validation in the zonemd.cc component. A malicious authoritative server can exploit this by sending a specially crafted zone, causing the Recursor process to crash. The attack requires the Recursor to be configured to fetch and cache zones from the attacker-controlled server. The vulnerability is addressed in versions 5.2.11, 5.3.8, and 5.4.3.

## Affected products

- PowerDNS Recursor 5.2.0 to 5.2.10, 5.3.0 to 5.3.7, 5.4.0 to 5.4.2

## Timeline

- 2026-06-25: disclosed: Initial advisory publication

## References

- [https://repo.powerdns.com/](https://repo.powerdns.com/)
- [https://docs.powerdns.com/recursor/security-advisories/powerdns-advisory-powerdns-2026-08.html](https://docs.powerdns.com/recursor/security-advisories/powerdns-advisory-powerdns-2026-08.html)

## Related threats

- [PowerDNS Recursor DNSSEC wildcard validation bypass in RRSIG processing](https://junglewise.ai/threats/cve-2026-52688-powerdns-recursor-dnssec-wildcard-validation-bypass-in-rrsig)
- [PowerDNS Recursor DNSSEC validation bypass in wildcard CNAME/DNAME records](https://junglewise.ai/threats/cve-2026-52686-powerdns-recursor-dnssec-validation-bypass-in-wildcard-cname)
- [PowerDNS Recursor TTL capping bypass in NS record refresh](https://junglewise.ai/threats/cve-2026-52684-powerdns-recursor-ttl-capping-bypass-in-ns-record-refresh)
- [PowerDNS Recursor DNSSEC validation failure via EDNS spoofing](https://junglewise.ai/threats/cve-2026-52690-powerdns-recursor-dnssec-validation-failure-via-edns-spoofing)
- [PowerDNS Recursor improper ZONEMD validation in ZoneToCache](https://junglewise.ai/threats/cve-2026-42390-powerdns-recursor-improper-zonemd-validation-in-zonetocache)