# CVE-2026-77775: Headroom Proxy Sends Upstream Requests to a Client-Supplied Base URL Without Address Validation

Status: published. Published: 2026-08-21. Updated: 2026-11-08.

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.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/headroomlabs-ai/headroom/pull/2207

## Affected products and versions

- Headroom Labs / Headroom (headroom-ai): ≥ 0; < 0.36.1 (affected, semver); 0.36.1 (unaffected, semver). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 3.1: 8.6 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N; source: CNA: VulnCheck

- CVSS 4.0: 7.7 (high); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N; source: CNA: VulnCheck

- CISA KEV: No listing in collected sources

- EPSS: 0.59% as of 2026-11-08; percentile 48.62%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-918

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/headroomlabs-ai/headroom/pull/2207 (CNA: VulnCheck; issue-tracking, patch)

- https://github.com/headroomlabs-ai/headroom/blob/v0.29.0/headroom/proxy/handlers/openai.py (CNA: VulnCheck; technical-description)

- https://github.com/headroomlabs-ai/headroom/blob/v0.36.1/headroom/proxy/upstream_guard.py (CNA: VulnCheck; technical-description)

- https://github.com/headroomlabs-ai/headroom (CNA: VulnCheck; product)

- https://www.vulncheck.com/advisories/headroom-proxy-sends-upstream-requests-to-a-client-supplied-base-url-without-address-validation (CNA: VulnCheck; third-party-advisory)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-77775; retrieved 2026-11-08; source updated 2026-11-08

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-77775; retrieved 2026-11-08; source updated Not reported

Revision: 8866039532c2c61ac37e9c8244f6d2529f708989b30d292323e58bbb5a71172c

Canonical: https://y2.dev/cve/CVE-2026-77775

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