CoreDNS DoH GET oversized dns= query parameter causes pre-validation CPU and memory amplification

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

• CVE-2026-32936: 0.67% estimated exploitation activity in the next 30 days; percentile 52.12 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary CoreDNS's DNS-over-HTTPS (DoH) GET path accepts oversized dns= query values and performs substantial request parsing, query unescaping, base64 decoding, and message unpacking work before returning 400 Bad Request. A remote, unauthenticated attacker can repeatedly send oversized DoH GET requests to /dns-query?dns=... and force high CPU usage, large transient allocations, elevated garbage-collection pressure, and increased resident memory consumption even though the requests are ultimately rejected. This is a denial-of-service issue caused by expensive pre-validation processing on the DoH GET path. Details The vulnerable flow is in plugin/pkg/doh/doh.go: - RequestToMsg() dispatches GET requests to requestToMsgGet(): - plugin/pkg/doh/doh.go:79-89 - requestToMsgGet() calls req.URL.Query(), extracts dns, and passes it directly to base64ToMsg(): - plugin/pkg/doh/doh.go:99-108 - base64ToMsg() decodes the full attacker-controlled value via b64Enc.DecodeString() and only then attempts…

Published by the source

28 Apr 2026, 22:43 UTC

Last modified by the source

12 Jun 2026, 19:25 UTC

Source last checked

26 Oct 2026, 15:23 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-63cw-r7xf-jmwr

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# Patch Next advisory brief: CVE-2026-32936

Advisory: CoreDNS DoH GET oversized dns= query parameter causes pre-validation CPU and memory amplification
IDs: CVE-2026-32936, GHSA-63cw-r7xf-jmwr
Record: https://patchnext.com/advisories/cve-2026-32936 (revision 1, source checked 26 Oct 2026, 15:23 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: github.com/coredns/coredns 1.14.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/coredns/coredns: affected < 1.14.3; fixed in 1.14.3

## Suggested inspection (read-only)
- Go github.com/coredns/coredns: 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 github.com/coredns/coredns.
- 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://github.com/advisories/GHSA-63cw-r7xf-jmwr (GitHub-reviewed advisory GHSA-63cw-r7xf-jmwr lists affected ranges: Go github.com/coredns/coredns >=0 <1.14.3)

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