# CVE-2026-77776: Headroom Proxy Treats the Client-Supplied x-headroom-user-id Header as an Authenticated Identity

> Attackers can impersonate other users by spoofing the x-headroom-user-id header to read or modify their LLM memory, particularly in exposed Docker deployments.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 21 Aug 2026
- **Updated:** 21 Aug 2026
- **Also known as:** GHSA-5vg3-c628-vf56

## What is CVE-2026-77776?

CVE-2026-77776 is a critical authentication bypass 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 derives the memory owner from the x-headroom-user-id request header. The header is read directly at several points in headroom/proxy/handlers/openai.py, including the chat completion and websocket paths, and nothing binds the value to the caller. A client can therefore name another user's identifier and read or write that user's stored LLM memory. The fix introduces a single resolve_memory_identity seam in headroom/proxy/identity.py that honors the header only for loopback or allowlisted callers and otherwise binds the identity to the proxy-token fingerprint or the operating system user. 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-639 (Authorization Bypass Through User-Controlled Key)

## Which versions are affected by CVE-2026-77776?


## How do I fix CVE-2026-77776?

No fix has been published for CVE-2026-77776 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-77776 being exploited?

There is no known exploitation of CVE-2026-77776 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77776 and fix it if it is affected.

What it is: CVE-2026-77776 is a critical authentication bypass 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.
Exploitation: There is no known exploitation of CVE-2026-77776 in the wild and no public exploit code.

Affected product: Headroom. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-77776/ (Markdown: https://insights.sbomify.com/CVE-2026-77776/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77776
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77776
- OSV: https://osv.dev/vulnerability/CVE-2026-77776

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-77776/
Summaries are generated and may contain mistakes; the official description above is the record.