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CVE-2026-40864 is a cross-site request forgery protection bypass in JupyterHub versions 4.1.0 through 5.4.4. XSRF validation incorrectly treats requests carrying the Sec-Fetch-Mode: no-cors header as same-origin, allowing cross-site requests to bypass XSRF checks on HTTP form endpoints. The JSON API is not affected. Affected actions include form-based endpoints used to spawn servers and accept server shares.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
This repository is a minimal proof-of-concept for CVE-2026-40864, an XSRF/CSRF bypass affecting JupyterHub 4.1.0 through versions before 5.4.5. The repo contains two files: a README describing the vulnerability, impact, affected endpoints, and usage steps; and a single exploit file, poc/csrf_spawn.html, which is the operational PoC. The exploit is not part of a larger framework. The PoC works by abusing JupyterHub's incorrect trust of the browser header state Sec-Fetch-Mode: no-cors. A cross-origin HTML form POST is treated by vulnerable JupyterHub as same-origin, so the XSRF check is skipped. The included HTML page auto-submits on load and sends a POST request to https://TARGET-JUPYTERHUB/hub/spawn with an empty _xsrf field. If opened by a browser session already authenticated to the target JupyterHub, it causes the victim's server to spawn without consent. The README also documents a variant targeting /hub/accept-share, which can force a victim to accept access to an attacker-controlled shared server. Repository structure is simple and purpose-built: README.md provides vulnerability context and operator instructions, while poc/csrf_spawn.html is the sole exploit artifact and likely entry point. There is no shell payload, persistence, or post-exploitation logic; this is a browser-based web exploit demonstrating unauthorized state-changing requests in an authenticated victim session.
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1 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.
No news coverage yet. Advisories and community discussion only.
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