JupyterHub has cross-origin form POSTs bypass XSRF (CWE-352)
## Summary JupyterHub's XSRF protection (updated in 4.1.0) inappropriately treated requests with `Sec-Fetch-Mode: no-cors` as same-origin requests, which they are not, bypassing XSRF checks. The JSON API is not affected, only HTTP form endpoints, such as `/hub/spawn` and `/hub/accept-share`, meaning attackers could trigger server spawn (but not access the server) and if the attacker is a JupyterHub user permitted to share access to their server, cause a user to accept a share and have access to the attacker's server. ## Patches Upgrade to JupyterHub 5.4.5. ## Mitigations If a reverse proxy is in use, drop requests to JupyterHub with `Sec-Fetch-Mode: no-cors`.
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Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2026-40864US | medium4.3 | Exploit | ||
JupyterHub is software that allows users to create a multi-user server for Jupyter notebooks. In versions 4.1.0 through 5.4.4, XSRF protection (updated in 4.1.0) inappropriately tr… | ||||
references
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