EUVD-2026-12092CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N
Lifecycle Timeline
3Description
LibreChat is a ChatGPT clone with additional features. From 0.8.2 to 0.8.2-rc3, The MCP (Model Context Protocol) OAuth callback endpoint accepts the redirect from the identity provider and stores OAuth tokens for the user who initiated the flow, without verifying that the browser hitting the redirect URL is logged in or that the logged-in user matches the initiator. An attacker can send the authorization URL to a victim; when the victim completes the flow, the victim’s OAuth tokens are stored on the attacker’s LibreChat account, enabling account takeover of the victim’s MCP-linked services (e.g. Atlassian, Outlook). This vulnerability is fixed in 0.8.3-rc1.
Analysis
LibreChat versions 0.8.2 through 0.8.2-rc3 contain an authentication bypass vulnerability in the Model Context Protocol (MCP) OAuth callback endpoint that allows attackers to steal OAuth tokens by tricking victims into completing an OAuth flow, resulting in account takeover of the victim's MCP-linked services like Atlassian and Outlook. No active exploitation is known (not in KEV), no POC is publicly available, and EPSS data is not yet available for this newly disclosed vulnerability.
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Remediation
Within 24 hours: Identify all LibreChat instances running versions 0.8.2 through 0.8.2-rc3 and document their usage scope and connected OAuth services. Within 7 days: Disable the MCP OAuth callback endpoint or restrict access via network controls if feasible; communicate security advisory to all LibreChat users warning against completing unexpected OAuth authorization prompts. …
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External POC / Exploit Code
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