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LibreChat EUVDEUVD-2026-39457

| CVE-2026-54030 CRITICAL
Origin Validation Error (CWE-346)
2026-06-25 GitHub_M
Information Disclosure Librechat
9.3
CVSS 3.1 · NVD
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Severity by source

Vendor (GitHub_M) PRIMARY
HIGH
qualitative
NVD
9.3 CRITICAL
AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
vuln.today AI
9.3 CRITICAL

Network OAuth flow with no attacker privileges but requires an operator to add the malicious server (UI:R); token theft crosses to another server (S:C) breaching confidentiality and enabling integrity actions, no availability impact.

3.1 AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:N/VA:N/SC:H/SI:H/SA:N

Primary rating from Vendor (GitHub_M).

CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

Lifecycle Timeline

7
Analysis Updated
Jun 30, 2026 - 00:13 vuln.today
v3 (cvss_changed)
Analysis Updated
Jun 30, 2026 - 00:13 vuln.today
v2 (cvss_changed)
Re-analysis Queued
Jun 30, 2026 - 00:07 vuln.today
cvss_changed
Severity Changed
Jun 30, 2026 - 00:07 NVD
HIGH CRITICAL
CVSS changed
Jun 30, 2026 - 00:07 NVD
8.0 (HIGH) 9.3 (CRITICAL)
Patch available
Jun 25, 2026 - 18:03 EUVD
Analysis Generated
Jun 25, 2026 - 17:16 vuln.today

DescriptionNVD

LibreChat is an enhanced ChatGPT clone that supports multiple AI providers. Prior to 0.8.5, LibreChat's MCP OAuth implementation does not validate that the resource parameter from OAuth Protected Resource metadata (RFC 9728) matches the configured MCP server URL, allowing a malicious MCP server to steal access tokens intended for a legitimate server. This vulnerability is fixed in 0.8.5.

AnalysisAI

Access-token theft in LibreChat before 0.8.5 lets a malicious MCP (Model Context Protocol) server hijack OAuth tokens minted for a legitimate server, because the client never checks that the RFC 9728 resource parameter matches the configured MCP server URL. Any LibreChat operator who connects their instance to an attacker-controlled MCP server can have the OAuth access tokens intended for a trusted server silently exfiltrated. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Stand up malicious MCP server
Delivery
Lure operator to add server
Exploit
Serve crafted RFC 9728 resource metadata
Execution
LibreChat skips resource validation
Persist
Capture token meant for legitimate server
Impact
Replay token against trusted server
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Vulnerability AssessmentAI

Exploitation Exploitation requires that LibreChat (prior to 0.8.5) be configured to use its MCP OAuth integration and that an operator/user connect the instance to an attacker-controlled MCP server - that act of trusting and adding the malicious server is the core prerequisite (reflected as UI:R in the CVSS vector). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment Signals are mixed and should be read together. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker stands up a malicious MCP server and lures a LibreChat administrator into adding it (e.g., advertised as a useful tool integration). When the operator initiates the OAuth flow, the rogue server returns Protected Resource metadata whose 'resource' value points at a legitimate server; LibreChat, not validating the resource against the configured URL, hands over or exposes the access token, which the attacker then replays against the trusted server. …
Remediation Vendor-released patch: upgrade to LibreChat 0.8.5, which adds validation that the OAuth Protected Resource metadata 'resource' parameter matches the configured MCP server URL; see the advisory at https://github.com/danny-avila/LibreChat/security/advisories/GHSA-gvpj-vm2f-2m23. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: Identify all LibreChat instances and current versions; isolate any running versions before 0.8.5 from connecting to new MCP servers. …

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EUVD-2026-39457 vulnerability details – vuln.today
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