CVE-2026-77776 (CVSS 9.1)

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.

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CVSS v3.1 Score

9.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS — Exploit Prediction

0.0035

Probability of exploitation

0.28%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-639 CWE-639

References

Other References

https://github.com/headroomlabs-ai/headroom https://github.com/headroomlabs-ai/headroom/blob/v0.29.0/headroom/proxy/handlers/openai.py https://github.com/headroomlabs-ai/headroom/blob/v0.36.1/headroom/proxy/identity.py https://github.com/headroomlabs-ai/headroom/pull/2207 https://www.vulncheck.com/advisories/headroom-proxy-treats-the-client-supplied-x-headroom-user-id-header-as-an-authenticated-identity

Frequently Asked Questions

What is CVE-2026-77776? +

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. It has a CVSS v3.1 base score of 9.1 (CRITICAL).

How severe is CVE-2026-77776? +

CVE-2026-77776 has a CVSS v3.1 score of 9.1 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0035, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-77776? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2026-77776