Executive brief
AdGuard Home is a network-wide tool used to block advertisements and tracking by managing DNS traffic. A vulnerability in how it handles certain encrypted DNS requests (DNS-over-QUIC) makes it easier for an attacker to predict or manipulate DNS responses. This could potentially allow an attacker to redirect users to malicious websites or disrupt internet connectivity by spoofing DNS data.
Technical details
A vulnerability exists in the client-triggered DNS-over-QUIC (DoQ) forwarding path to UDP upstreams in AdGuard Home (prior to 0.107.75) and dnsproxy (prior to 0.81.2). The backend DNS transaction ID (txid) is not properly randomized and instead collapses to a deterministic value of 0. Additionally, the implementation exposes a source-port oracle via ICMP error messages, allowing an attacker to identify the backend UDP source port. By reducing the entropy of the (txid, source-port) tuple to just the source port, the software becomes significantly more susceptible to off-path DNS cache poisoning and forgery attacks similar to 'SAD DNS'.
Affected products
- AdguardTeam AdGuard Home < 0.107.75
- AdguardTeam dnsproxy < 0.81.2
Timeline
- 2026-04-25: other: Vulnerability reproduced by researchers
- 2026-05-19: advisory: GitHub Security Advisory published
- 2026-07-15: disclosed: CVE-2026-47703 published to NVD