CVE-2026-20205: Splunk MCP Server Information Disclosure

CVE-2026-20205 Overview

A sensitive information disclosure vulnerability exists in Splunk MCP Server app versions below 1.0.3 that allows privileged users to view session and authorization tokens in clear text. Users who hold a role with access to the Splunk _internal index or possess the high-privilege capability mcp_tool_admin could exploit this vulnerability to extract sensitive authentication credentials from log files.

Critical Impact

Exposure of session and authorization tokens in clear text could allow attackers with administrative access to hijack user sessions, escalate privileges, or gain unauthorized access to protected resources within the Splunk environment.

Affected Products

• Splunk MCP Server app versions below 1.0.3

Discovery Timeline

• April 15, 2026 - CVE CVE-2026-20205 published to NVD
• April 15, 2026 - Last updated in NVD database

Technical Details for CVE-2026-20205

Vulnerability Analysis

This vulnerability is classified as CWE-532 (Insertion of Sensitive Information into Log File), a common security weakness where applications inadvertently write sensitive data such as passwords, tokens, or API keys to log files. In this case, the Splunk MCP Server app logs session and authorization tokens in clear text, making them accessible to users with sufficient privileges to read internal indexes or log files.

The vulnerability requires either local access to the log files on the Splunk server or administrative access to internal indexes. By default, only the admin role receives access to the _internal index, limiting the attack surface to privileged users. However, in environments where roles have been misconfigured or where internal index access has been granted more broadly, the risk of exploitation increases significantly.

Root Cause

The root cause of this vulnerability is improper handling of sensitive authentication data during logging operations. The Splunk MCP Server app fails to sanitize or mask session and authorization tokens before writing them to log files, resulting in clear text exposure of these credentials. This represents a failure to follow secure logging practices that require redaction of sensitive information before persistence.

Attack Vector

Exploitation of this vulnerability requires network access and high privileges. An attacker would need to either:

1. Gain local access to the Splunk server file system to read log files directly
2. Obtain a role with access to the _internal index through Splunk's web interface or API
3. Acquire the mcp_tool_admin capability which grants elevated permissions

Once access is obtained, the attacker can search through logs or index data to locate and extract clear text session and authorization tokens belonging to other users. These tokens could then be used for session hijacking, privilege escalation, or unauthorized access to connected systems.

The vulnerability is exploited through standard Splunk search queries or direct file system access rather than through specialized exploit code.

Detection Methods for CVE-2026-20205

Indicators of Compromise

• Unusual search queries targeting the _internal index, particularly those filtering for authentication-related fields
• Unexpected access patterns to MCP Server log files on the file system
• Anomalous login activity or session hijacking attempts using tokens extracted from logs
• Users with the mcp_tool_admin capability performing searches they normally wouldn't conduct

Detection Strategies

• Monitor and audit all queries executed against the _internal index for patterns indicating token extraction
• Implement file integrity monitoring on Splunk log directories to detect unauthorized access
• Enable detailed audit logging for users with high-privilege capabilities such as mcp_tool_admin
• Configure alerts for bulk searches or exports from internal indexes

Monitoring Recommendations

• Review role assignments and ensure the _internal index access is restricted to administrator-level roles only
• Regularly audit user capabilities to identify any accounts with mcp_tool_admin that should not have this privilege
• Implement session monitoring to detect potential token reuse from unexpected locations or devices

How to Mitigate CVE-2026-20205

Immediate Actions Required

• Upgrade Splunk MCP Server app to version 1.0.3 or later immediately
• Review all roles and capabilities on your Splunk instance and restrict internal index access to administrator-level roles only
• Audit and revoke the mcp_tool_admin capability from any users who do not require it
• Rotate all session and authorization tokens that may have been exposed in logs

Patch Information

Splunk has released version 1.0.3 of the MCP Server app which addresses this vulnerability. The patch prevents session and authorization tokens from being written to log files in clear text. For detailed information about the fix and upgrade instructions, refer to the Splunk Security Advisory SVD-2026-0407.

Organizations should also consult the Splunk documentation on Define roles on the Splunk platform with capabilities and Connecting to MCP Server and Admin settings for guidance on properly configuring access controls.

Workarounds

• Restrict access to the _internal index to only essential administrator roles until the patch can be applied
• Remove or limit the mcp_tool_admin capability to reduce the number of accounts that could potentially exploit this vulnerability
• Implement network segmentation to limit local file system access to Splunk servers
• Consider implementing log rotation and secure deletion of older logs that may contain exposed tokens

# Example: Review current role assignments in Splunk
# Navigate to Settings > Roles in Splunk Web
# Or use the REST API to audit roles with _internal index access:
curl -k -u admin:password https://localhost:8089/services/authorization/roles -d output_mode=json