Home Assistant Green flaw lets local attackers force internal requests

Home Assistant Green is vulnerable to a Server-Side Request Forgery (SSRF) flaw that lets an unauthenticated attacker on the same local network trick the device into making HTTP requests to arbitrary hosts, including internal services. The problem was disclosed in a GitHub security advisory, GHSA-4ghv-53cq-7wp3, published on 22 September 2026 and tracked as CVE-2026-91129.

According to the advisory, the flaw sits in Home Assistant's IPP integration, which handles printers. Home Assistant listens for mDNS service announcements on port 5353. mDNS is a protocol used by devices to advertise themselves on a local network. When a service of type _ipp._tcp.local is discovered, the IPP integration processes it automatically, without any user interaction or authentication.

The advisory says the integration's zeroconf handler extracts the host, port and base path directly from the discovery information without validation. Those values are then passed to a function that constructs an HTTP request to the advertised host. The core issue, according to the advisory, is that the HTTP session blindly follows redirects. That allows an attacker to point the request at 127.0.0.1 or other internal services that are not otherwise reachable over the network.

The advisory describes how the attack works. An attacker crafts an mDNS response advertising a fake IPP printer that points to the attacker's own IP address. Home Assistant then connects to the attacker's HTTP server. The server responds with a 302 redirect to any internal endpoint, causing Home Assistant to make the request on the attacker's behalf.

The advisory includes a proof-of-concept exploit. It uses a Python script that builds and sends a spoofed mDNS response advertising the fake printer, alongside a small HTTP server that replies to the incoming request with a 302 redirect to an internal address and port. The advisory lists two prerequisites: an attacker machine on the same local network as the Home Assistant Green device, and Python 3 with the script's dependencies.

The steps set out in the advisory are that the script starts an HTTP server that responds with a redirect to an internal service, a crafted mDNS response is sent to Home Assistant advertising a fake IPP printer pointing to the attacker's IP, and Home Assistant's IPP integration then follows the chain.

The advisory does not state that the flaw has been exploited against real users. The structured record for the disclosure lists its status as reported and gives no date on which any incident occurred. The root cause is recorded as a misconfiguration, and the severity is rated three on the record's scale.

The advisory attributes the vulnerability to the way discovery information is trusted and redirects are followed automatically. It does not describe a patch or mitigation in the material provided. Readers running Home Assistant Green should consult the vendor's advisory directly for the current status and any available fix.