Gradio versions before 6.15.0 contain a cookie injection vulnerability that enables remote attackers to perform cross-Space session fixation. The issue arises because a shared module-level HTTP client in the reverse proxy endpoint stores a parent-domain cookie returned by an attacker-controlled Space. This cookie is then automatically included in all subsequent proxy requests to other legitimate Spaces, impacting all users of the Gradio deployment. The vulnerability has a CVSS 4.0 score of 7.6, indicating high severity. No patch or official remediation level has been published as of the data provided.

Successful exploitation allows an attacker controlling any Hugging Face Space to inject a parent-domain cookie that is reused by the shared HTTP client for all users of the Gradio deployment. This can lead to session fixation across different Spaces, potentially enabling unauthorized session access or manipulation. The vulnerability affects all users of the same Gradio deployment due to the shared client behavior. There are no known exploits in the wild at this time.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since no official fix or remediation level is provided, users should monitor vendor communications for updates. Until a patch is available, consider isolating Spaces or limiting shared client usage if possible to reduce exposure.