CVE-2026-47703: AdGuard Home: DoQ-to-UDP State Reduction and Source-Port Oracle

June 4, 2026 (updated July 20, 2026)

This report covers the client-triggered DoQ forwarding path in:

dnsproxy v0.81.2 (adguard/dnsproxy:v0.81.2)
AdGuard Home v0.107.74 (adguard/adguardhome:latest, image version label v0.107.74)

The issue was reproduced on 2026-04-25 with the products configured through their documented DoQ listener and plain UDP upstream surfaces. The scope is the internal backend UDP hop created when a DoQ query is forwarded to a udp:// upstream.

On that path, the backend DNS ID is not preserved as an independent source of entropy. For both products, the backend observer saw dns_id=0 for every sampled client-triggered query on the tested path. Repeated reruns then showed the same txid=0 behavior and the same positive source-port oracle on every sampled run. A separate quoted-port ICMP oracle distinguished the correct backend UDP source port from a wrong one with a stable, client-visible behavior change.

Attached evidence:

References

Code Behaviors & Features

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