Information disclosure in LibreChat - CVE-2026-31951
Published: April 27, 2026
Vulnerability identifier: #VU128117
CSH Severity: Low
CVSS v4: 6.8 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-31951
CWE-ID: CWE-200
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote user to disclose sensitive information.
The vulnerability exists due to improper access control in MCP server header processing when handling tool calls to user-created MCP servers. A remote user can create a malicious MCP server with crafted header placeholders to disclose sensitive information.
User interaction is required, and credential substitution in headers occurs during subsequent tool calls rather than initial connection or inspection. OAuth token exposure requires OpenID SSO to be configured and the victim to be authenticated through it.
Affected software
LibreChat
How to mitigate CVE-2026-31951
Install security update from vendor's website.
LibreChat - update to 0.8.3 rc2