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CVE-2026-77776 – Cross-User Memory Disclosure/Manipulation via Header Spoofing – Headroom (headroom-

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Summary

CVE-2026-77776 is a critical authorization bypass vulnerability (CWE-639: Authorization Bypass Through User-Controlled Key) affecting Headroom, an open-source LLM context/memory proxy distributed as the headroom-ai package. The proxy’s OpenAI-compatible request handler trusts the client-supplied x-headroom-user-id HTTP header as a caller’s identity without binding it to any authenticated session, allowing a remote, unauthenticated attacker to read or write another user’s stored LLM memory simply by naming their user identifier. The issue carries a CVSS v3.1 base score of 9.1 (Critical).

Technical details

  • Root cause: headroom/proxy/handlers/openai.py (and related memory-handling code in headroom/proxy/memory_handler.py and headroom/memory/easy.py) reads the x-headroom-user-id header directly and uses it as the identity key for the memory store, without verifying that the header value corresponds to the actual authenticated caller.
  • Trigger conditions: Any client able to reach the Headroom proxy’s OpenAI-compatible API endpoint can set an arbitrary x-headroom-user-id value in the request header to impersonate another user’s memory namespace.
  • Compounding factor: The project’s reference Docker Compose configuration exposes the proxy to the network without requiring a proxy authentication token, making the flaw remotely exploitable by default in that deployment pattern.
  • Attack vector: Network (AV:N), low attack complexity, no privileges or user interaction required.
  • Impact: Confidentiality impact is high — an attacker can read another user’s persisted LLM conversation/memory data by supplying their user ID. The CVSS vector for this CVE (C:H/I:H/A:N) also reflects an integrity impact, consistent with the ability to write/poison another user’s stored memory, while availability is not affected.

Affected software

  • Headroom (headroom-ai PyPI package) versions 0 through 0.36.0
  • Fixed in version 0.36.1 and later

Severity

  • CVSS v3.1 Base Score: 9.1 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Mitigation and recommended actions

  • Immediate: Upgrade Headroom to version 0.36.1 or later, which introduces a centralized resolve_memory_identity() function that only honors the x-headroom-user-id header for loopback or explicitly allowlisted callers; for all other (remote) requests, identity is bound to the proxy-token fingerprint instead of the client-supplied header.
  • If unable to patch immediately:
    • Require and enforce a proxy authentication token (HEADROOM_PROXY_TOKEN) for all deployments — do not run the reference Docker Compose configuration without setting this value.
    • Restrict network exposure of the Headroom proxy so it is reachable only from trusted/loopback hosts, and avoid publishing its ports directly to untrusted networks.
    • Audit any existing deployments for evidence of cross-user memory access via manipulated x-headroom-user-id headers before patching.

References

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