CVE-2026-16496 in terraform-mcp-server
Summary
by MITRE • 07/28/2026
The terraform-mcp-server before version 1.1.0 is vulnerable to an authorization bypass in the streamable-HTTP stateful transport mode that may allow a user who obtains another user's MCP session ID to have their tool calls executed using that user's Terraform credentials. This vulnerability, CVE-2026-16496, is fixed in terraform-mcp-server 1.1.0.
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Analysis
by VulDB Data Team • 07/29/2026
The terraform-mcp-server vulnerability CVE-2026-16496 represents a critical authorization bypass flaw that undermines the security of stateful transport operations within the server's HTTP streaming capabilities. This vulnerability specifically affects versions prior to 1.1.0 and exploits a fundamental weakness in session management that allows unauthorized users to impersonate legitimate session holders. The issue manifests when an attacker gains access to another user's MCP session identifier, enabling them to execute tool calls with the target user's Terraform credentials without proper authentication. This authorization bypass directly violates core security principles of least privilege and proper access control enforcement.
The technical implementation flaw resides in how the terraform-mcp-server handles session validation during streamable HTTP stateful transport operations. When a user establishes a session, the server generates an MCP session ID that should serve as the primary authentication token for subsequent tool call executions. However, the vulnerability demonstrates that the authorization check mechanism fails to properly validate session ownership or enforce proper access controls when processing tool calls through the streaming transport mode. This weakness creates a scenario where any user possessing a valid session ID can execute operations that should be restricted to the legitimate session owner, effectively allowing privilege escalation and credential misuse.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential compromise of sensitive infrastructure configurations and deployment operations. When an attacker successfully exploits this authorization bypass, they gain the ability to execute Terraform commands with the privileges and credentials of the victim user, potentially leading to unauthorized infrastructure provisioning, configuration changes, or even complete system compromise. The severity is amplified by the fact that MCP session IDs are typically long-lived tokens that may persist beyond typical session timeouts, providing extended windows for exploitation. This vulnerability particularly affects environments where multiple users share administrative or production-level Terraform credentials, as the attacker's access level matches that of the compromised user.
Mitigation strategies for CVE-2026-16496 require immediate implementation of version 1.1.0 or later where the authorization bypass has been resolved. Organizations should conduct comprehensive audits of existing session management practices and implement additional monitoring for unauthorized session usage patterns. The fix addresses the root cause by strengthening session validation mechanisms to ensure that each tool call execution properly verifies session ownership before authorizing operations against Terraform credentials. Security teams should also consider implementing session token rotation policies, enhanced logging of session-based activities, and network-level controls to limit access to MCP endpoints. This vulnerability aligns with CWE-285 which addresses improper authorization in security-critical applications, and represents a clear violation of ATT&CK technique T1078 for valid accounts and privilege escalation through session hijacking. Organizations utilizing the terraform-mcp-server must ensure complete deployment of the patched version across all environments to prevent exploitation of this authorization bypass vulnerability.
The remediation process should include thorough testing of the updated server configuration to verify that proper authorization controls are now enforced during streaming HTTP operations. Security administrators should also review and update their incident response procedures to detect potential exploitation attempts through monitoring for unusual tool call patterns or unauthorized session access. Regular security assessments of stateful transport mechanisms within infrastructure automation tools are recommended to prevent similar authorization bypass vulnerabilities from emerging in other components of the deployment pipeline.