CVE-2026-54030Public exploitNetwork attack vector

Access-token theft via unvalidated OAuth resource

Published Jun 25, 2026 · Updated Jun 25, 2026

OAuth resource validation failure in LibreChat before 0.8.5 allows remote attackers to steal MCP access tokens through malicious metadata. In packages/api/src/mcp/oauth/handler.ts, the OAuth handler copies the metadata resource URL into the authorization request without matching it to the configured MCP server. Exploitation requires a victim to configure an attacker-controlled OAuth-protected MCP server and complete its legitimate-looking authorization flow, after which the server receives a token usable to impersonate the victim at the legitimate MCP service.

CVSS severity8.0
High
EPSS probability0.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

OAuth resource validation failure in LibreChat before 0.8.5 allows remote attackers to steal MCP access tokens through malicious metadata. In packages/api/src/mcp/oauth/handler.ts, the OAuth handler copies the metadata resource URL into the authorization request without matching it to the configured MCP server. Exploitation requires a victim to configure an attacker-controlled OAuth-protected MCP server and complete its legitimate-looking authorization flow, after which the server receives a token usable to impersonate the victim at the legitimate MCP service.

The record

CVE
CVE-2026-54030
Published
Jun 25, 2026
Updated
Jun 25, 2026
Vendor
Danny Avila
Product
LibreChat
Classifications
CWE-346, T1528
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 0.8.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Danny Avila · LibreChatversion=< 0.8.5

Published CVSS scores

8.0GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N
9.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-346Origin Validation Error
T1528Steal Application Access Token

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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