Security Bulletin
Summary
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.
Vulnerability Details
CVEID: CVE-2026-16496
DESCRIPTION: In the affected versions, the per-session Terraform client cache used the MCP session ID as its sole lookup key and did not bind cached clients to the token that created them. When a subsequent request arrived carrying a known session ID, the server returned the cached client for that session without verifying that the current request's token matched the one used to create the cache entry. A user who obtained another user's session ID could supply it in their own request and have their tool calls executed using the victim's cached Terraform client and bearer token, potentially gaining access to the victim's Terraform organizations, workspaces, variables, and other resources within the scope of that token's permissions. The issue affects only deployments using stateful streamable-HTTP mode, which is the default when running the server centrally; stdio mode and stateless HTTP mode are not affected by this issue.
CWE: CWE-384: Session Fixation
CVSS Source: HashiCorp Inc.
CVSS Base score: 8.9
CVSS Vector: (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L)
Affected Products and Versions
| Affected Product(s) | Version(s) |
| terraform-mcp-server | affected from 0.3.0 up to 1.1.0 |
Remediation/Fixes
Customers should evaluate the risk associated with this issue and consider upgrading to terraform-mcp-server 1.1.0. Operators who cannot upgrade immediately and are running centralized streamable-HTTP deployments should restrict access to trusted users and treat the MCP session ID as a sensitive value.
Get Notified about Future Security Bulletins
References
Link to HashiCorp Security Bulletin: https://discuss.hashicorp.com/t/hcsec-2026-23-multiple-vulnerabilities-impacting-hashicorp-terraform-mcp-server/77606
Acknowledgement
This issue was reported to HashiCorp by Juan Pablo Martinez Kuhn of Coinspect.
Change History
28 Jul 2026: Initial Publication
*The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin.
Disclaimer
According to the Forum of Incident Response and Security Teams (FIRST), the Common Vulnerability Scoring System (CVSS) is an "industry open standard designed to convey vulnerability severity and help to determine urgency and priority of response." IBM PROVIDES THE CVSS SCORES ""AS IS"" WITHOUT WARRANTY OF ANY KIND, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. CUSTOMERS ARE RESPONSIBLE FOR ASSESSING THE IMPACT OF ANY ACTUAL OR POTENTIAL SECURITY VULNERABILITY. In addition to other efforts to address potential vulnerabilities, IBM periodically updates the record of components contained in our product offerings. As part of that effort, if IBM identifies previously unidentified packages in a product/service inventory, we address relevant vulnerabilities regardless of CVE date. Inclusion of an older CVEID does not demonstrate that the referenced product has been used by IBM since that date, nor that IBM was aware of a vulnerability as of that date. We are making clients aware of relevant vulnerabilities as we become aware of them. "Affected Products and Versions" referenced in IBM Security Bulletins are intended to be only products and versions that are supported by IBM and have not passed their end-of-support or warranty date. Thus, failure to reference unsupported or extended-support products and versions in this Security Bulletin does not constitute a determination by IBM that they are unaffected by the vulnerability. Reference to one or more unsupported versions in this Security Bulletin shall not create an obligation for IBM to provide fixes for any unsupported or extended-support products or versions.
Document Location
Worldwide
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Document Information
Modified date:
28 July 2026
Initial Publish date:
28 July 2026
UID
ibm17281661