CVE-2026-31951
LibreChat's MCP Server Header Injection Enables OAuth Token Theft
CVSS Score
6.8
EPSS Score
0.0%
EPSS Percentile
9th
LibreChat is a ChatGPT clone with additional features. In versions 0.8.2-rc1 through 0.8.3-rc1, user-created MCP (Model Context Protocol) servers can include arbitrary HTTP headers that undergo credential placeholder substitution. An attacker can create a malicious MCP server with headers containing `{{LIBRECHAT_OPENID_ACCESS_TOKEN}}` (and others), causing victims who call tools on that server to have their OAuth tokens exfiltrated. Version 0.8.3-rc2 fixes the issue.
| CWE | CWE-200 |
| Vendor | danny-avila |
| Product | librechat |
| Published | Mar 27, 2026 |
| Last Updated | Mar 31, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:N/A:N Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
Required
Scope
Changed
Confidentiality
High
Integrity
None
Availability
None
Affected Versions
danny-avila / LibreChat
>= v0.8.2-rc1, <= v0.8.3-rc1