CVE-2026-76286 in MCP Server
Summary
by MITRE • 10/08/2026
In Splunk MCP Server versions below 1.2.1, Splunk MCP Server could send the Splunk platform authentication token of a user who runs a custom Application Programming Interface (API) tool to the URL configured for that tool. If another user controls that URL, they could capture the token and use it to access data and perform actions as the user who ran the tool. Successful exploitation requires a user who holds a role that contains the mcp_tool_execute capability to run a custom API tool configured by another user. For more information see Configure the Splunk MCP Server (https://help.splunk.com/en/splunk-enterprise/mcp-server-for-splunk-platform/1.2/configure-the-splunk-mcp-server) and Managing custom tools in Splunk MCP Server (https://help.splunk.com/en/splunk-enterprise/mcp-server-for-splunk-platform/1.2/managing-custom-tools-in-splunk-mcp-server) in the Splunk documentation.
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Analysis
by VulDB Data Team • 10/08/2026
The vulnerability identified in Splunk Management Command Protocol (MCP) Server versions prior to 1.2.1 represents a critical information disclosure and privilege escalation flaw rooted in improper handling of authentication credentials during external API interactions. The core technical deficiency lies in the mechanism by which the MCP server processes requests for custom Application Programming Interface tools. When an authenticated user executes a custom tool, the system automatically injects that user's Splunk platform authentication token into the HTTP request headers sent to the URL configured within the tool definition. This behavior is designed to facilitate seamless integration with external services but fails to implement adequate safeguards against malicious configuration of those target URLs. Consequently, if the endpoint defined in the custom tool configuration is under the control of an attacker or a compromised system, it can intercept and capture these sensitive authentication tokens. The token serves as a bearer credential that grants full access to the Splunk platform on behalf of the user who initiated the request, effectively bypassing standard access controls for any subsequent operations performed using this stolen credential.
The operational impact of this vulnerability is severe, allowing an attacker with limited initial privileges to escalate their rights significantly within the Splunk environment. Exploitation requires a specific precondition: the attacker must be able to influence or control the URL endpoint associated with a custom tool that another user executes. In many enterprise deployments, users possess roles containing the mcp_tool_execute capability, which allows them to run tools configured by administrators or other privileged users. If an adversary can manipulate the configuration of such a tool—either through social engineering, account compromise, or misconfiguration—they can force legitimate users with higher privileges to execute requests that leak their session tokens. Once captured, these tokens enable the attacker to impersonate the victim user, access restricted data sets, modify configurations, and perform administrative actions without detection by standard authentication logs, as the activity appears to originate from a valid, authorized session.
This vulnerability aligns closely with CWE-200, which classifies exposure of sensitive information to an unauthorized actor, specifically within the context of API security failures where credentials are transmitted in plaintext or to untrusted endpoints. Furthermore, it maps directly to MITRE ATT&CK technique T1556.004, known as Modifying Application Access Control, and potentially T1078, Valid Accounts, as the attacker leverages stolen valid credentials to maintain persistence and move laterally within the environment. The flaw highlights a broader industry challenge in integrating third-party tools where trust boundaries are not strictly enforced between internal authentication systems and external service endpoints. Security architects must recognize that any mechanism automatically forwarding user tokens to configurable URLs introduces significant risk if input validation and destination verification are insufficient.
Mitigation strategies for this vulnerability primarily involve upgrading the Splunk MCP Server software to version 1.2.1 or later, where these issues have been addressed by implementing stricter controls over token transmission and URL validation. In environments where immediate patching is not feasible, administrators should enforce strict governance over custom tool configurations, ensuring that only trusted, internal endpoints are permitted for API integration. Additionally, network segmentation can be employed to restrict outbound traffic from Splunk servers to known safe destinations, preventing tokens from reaching attacker-controlled domains. Implementing robust monitoring and alerting on unusual authentication patterns or token usage anomalies can also help detect exploitation attempts early. Organizations must review their MCP tool configurations regularly to ensure that no custom tools point to external or unverified URLs, thereby eliminating the attack vector entirely until a permanent software fix is applied.