Executive brief
CoreDNS is a widely used DNS server that helps translate human-readable domain names into IP addresses. A vulnerability in its DNS-over-HTTPS (DoH) feature allows an unauthenticated attacker to overwhelm the server by sending specially crafted, oversized requests. This can lead to high CPU and memory usage, potentially causing the service to slow down or crash, which would disrupt internet connectivity for users relying on that server.
Technical details
A denial-of-service (DoS) vulnerability exists in CoreDNS versions prior to 1.14.3 within the DNS-over-HTTPS (DoH) GET request handler. While the POST path implements a bounded read using http.MaxBytesReader (limited to 64KB), the GET path lacks equivalent size validation for the 'dns=' query parameter. An unauthenticated remote attacker can send oversized base64-encoded DNS queries, forcing the server to perform URL unescaping, base64 decoding, and DNS message unpacking before the request is eventually rejected. This results in uncontrolled resource consumption (CWE-400), characterized by high CPU usage, large transient memory allocations, and increased garbage collection pressure. The issue is resolved in version 1.14.3 by implementing proper size checks on the GET path.
Affected products
- CoreDNS CoreDNS < 1.14.3
Timeline
- 2026-04-22: patched: Version 1.14.3 released
- 2026-04-25: advisory: GitHub Security Advisory GHSA-63cw-r7xf-jmwr published
- 2026-05-05: disclosed: CVE-2026-32936 published to NVD