CVE-2026-31951

LibreChat's MCP Server Header Injection Enables OAuth Token Theft

State: Published
Severity: 6.8 Medium
Published: Mar 27, 2026
Updated: Mar 31, 2026
Reserved: Mar 10, 2026

Description

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.

Scores

CVSS	Score	Vector	Source
3.1	6.8 Medium	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:N/A:N	GitHub_M

Weaknesses

CWE-200 Exposure of Sensitive Information to an Unauthorized Actor

Affected Products

Product	Versions
LibreChatdanny-avila	>= v0.8.2-rc1, <= v0.8.3-rc1Affected

References

https://github.com/danny-avila/LibreChat/security/advisories/GHSA-pmw7-gqwj-f954

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