CVE-2026-77775 Headroom Proxy Sends Upstream Requests to a Client-Supplied Base URL Without Address Validation
Attackers can force the proxy to send requests to internal or cloud metadata services via a client-supplied header, disclosing sensitive data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-77775?
CVE-2026-77775 is a high-severity server-side request forgery vulnerability in Headroom, published on 21 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Headroom's LLM proxy lets a client choose the upstream destination with the x-headroom-base-url request header. _resolve_openai_upstream_base in headroom/proxy/handlers/openai.py accepts the header value, requires only that it parse with an http or https scheme and a hostname, and returns it for use as the upstream base; _select_passthrough_base_url in headroom/providers/proxy_routes.py reads the same header for the passthrough routes. No check rejects loopback, link-local, or RFC 1918 destinations, and because the component is a proxy the upstream response is returned to the caller, so the request reaches internal services and cloud metadata addresses and their responses are disclosed. The Authorization header accompanying the request is forwarded unchanged to the caller-designated host. The pip console script binds 127.0.0.1 by default, but the reference docker-compose.yml ships --host 0.0.0.0 with published ports and no required HEADROOM_PROXY_TOKEN, which the server itself warns about at startup, so a deployment following the shipped compose exposes the affected data-plane routes to the network without authentication.
Weakness: CWE-918
Which versions are affected by CVE-2026-77775?
How do I fix CVE-2026-77775?
No fix has been published for CVE-2026-77775 yet. Limit exposure of the affected software until one is available.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-77775 being exploited?
There is no known exploitation of CVE-2026-77775 in the wild and no public exploit code.
Sources
Also known as GHSA-4j5r-9p93-j2px.