Cyber & AI intelligence
Wasteland.
Briefs indexed2425
Issues26
Published Mondays07:30 CT
⚡ Active KEV CVE-2026-85695 2026-09-04

CVE-2026-85695: Unauthenticated Worker Registration in FastChat Enables Model Spoofing and SSRF

"FastChat versions up to and including 0.2.36 expose an unauthenticated `/register_worker` endpoint that lets remote attackers register arbitrary workers, hijack model traffic, and pivot into internal networks."

FastChat versions up to and including 0.2.36 expose an unauthenticated /register_worker endpoint that lets remote attackers register arbitrary workers, hijack model traffic, and pivot into internal networks.

What Is It

CVE-2026-85695 is an authentication bypass (CWE-306, Missing Authentication for Critical Function) in the FastChat controller's /register_worker endpoint. The endpoint accepts worker registrations without any authentication, allowing an unauthenticated remote attacker to register arbitrary worker addresses with the controller. Because the controller then dispatches requests to those attacker-supplied addresses, the flaw doubles as a server-side request forgery primitive.

The CVSS 3.1 base score of 9.4 (Critical): vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L, and the CVSS 4.0 score of 9.3 come from VulnCheck as the assigning source, not from NVD. The record is still in Received status, so NVD has not completed its own analysis or published an independent score; the numbers above should be read as the CNA's assessment. The vulnerability is network-reachable, requires no privileges and no user interaction, and has low attack complexity. CISA's SSVC evaluation marks it automatable: yes with total technical impact.

Why It Matters

Two attack paths follow directly from the registration bypass. First, an attacker can register a malicious worker under a legitimate victim model name, causing the controller to route real traffic to attacker-controlled infrastructure; intercepting user prompts, uploaded images, and model responses in transit. Second, the arbitrary-address registration lets an attacker probe internal network ports across the worker mesh, turning the controller into an internal scanner from outside the perimeter.

CISA's SSVC data records exploitation status as none, and there is no CISA KEV entry for this CVE in the supplied source material; active exploitation is not confirmed. The automatable-yes rating still means mass exploitation is trivially scriptable if that changes.

What's Vulnerable

The vulnerable code path is in fastchat/serve/controller.py.

Patch Status

No fixed version, patch, or vendor remediation guidance is present in the supplied advisory record, and no CISA KEV required-action or due date applies. The CVE is in Received status (published 2026-09-04, source VulnCheck), meaning the record may still change as NVD enrichment completes. Operators should treat any internet-exposed FastChat controller as at risk and restrict network access to the controller until vendor guidance is available; track the linked GitHub issue for fix status.

Sources