MediumVulnerabilityLLM-specific

CVE-2026-31951: LibreChat OAuth token exfiltration through user-created MCP server headers

Source: NVD(opens in a new tab)
Identifier: CVE-2026-31951
Published: March 27, 2026
Record updated: October 9, 2026

Known exploitation: Not listed in the CISA Known Exploited Vulnerabilities catalog at the last check.
EPSS: 0.3%

Summary

CVE-2026-31951 affects LibreChat versions 0.8.2-rc1 through 0.8.3-rc1. User-created MCP (Model Context Protocol) servers can set arbitrary HTTP headers that undergo credential placeholder substitution, so a malicious server using `{{LIBRECHAT_OPENID_ACCESS_TOKEN}}` in its headers can exfiltrate the OAuth tokens of users who call tools on that server. The weakness is classified as CWE-200, Exposure of Sensitive Information to an Unauthorized Actor.

Mitigation

Fixed in 0.8.3-rc2.

Details

Scores and exploitation

CVSS score: 6.8(medium)
CVSS vector: 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
EPSS: 0.3%Estimated probability that this CVE is exploited in the next 30 days, from the FIRST Exploit Prediction Scoring System. Read on November 8, 2026.
Disclosure date: March 27, 2026

Weaknesses and techniques

Weakness (CWE): CWE-200
Attack pattern (CAPEC): CAPEC-116

Classification

Attack type: Other
Attack sophistication: Moderate
AI component targeted: Plugin
Impact: Confidentiality
Labels: security

How this record was produced

Summaries, mitigations and labels on this page are generated automatically from the source. The linked source is authoritative. The source gives this advisory a description and no title, so the title above is a headline generated from the source text.

Original source: https://nvd.nist.gov/vuln/detail/CVE-2026-31951

First tracked: March 28, 2026 at 02:07 AM ET, from NVD/CVE Database

Classifier: claude-haiku-5-5, prompt v4

Classifier confidence: 90% (self-assessed)

Topics

Model Context Protocol

Summary

Mitigation

Topics

Related items