CVE-2026-27826
MCP Atlassian
- Severity
- High
- Published
- March 10, 2026
- Last modified
- June 17, 2026
MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to version 0.17.0, an unauthenticated attacker who can reach the mcp-atlassian HTTP endpoint can force the server process to make outbound HTTP requests to an arbitrary attacker-controlled URL by supplying two custom HTTP headers without an `Authorization` header. No authentication is required. The vulnerability exists in the HTTP middleware and dependency injection layer — not in any MCP tool handler - making it invisible to tool-level code analysis. In cloud deployments, this could enable theft of IAM role credentials via the instance metadata endpoint (`169[.]254[.]169[.]254`). In any HTTP deployment it enables internal network reconnaissance and injection of attacker-controlled content into LLM tool results. Version 0.17.0 fixes the issue.
CVSS vector CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N
Weakness
- CWE-918 Server-side request forgery
References
- github.comPatch
- github.comExploitVendor Advisory
Listed in
More MCP Atlassian CVEs
Validate_url_for_ssrf has a backslash authority confusion because it interprets the authority differently from the Requests connection layer in the header-based Jira and Confluence URL authentication flow.
The OAuth error query parameter is passed to CallbackHandler._send_response in oauth_setup.py and interpolated into an HTML page without escaping.
Validate_safe_path defaults its base directory to os.getcwd(), and affected Confluence attachment call sites omit base_dir, allowing attacker-selected writes within the working directory.
The Jira and Confluence attachment upload tools treat caller-controlled file_path values as trusted server-local paths.
The remediation for CVE-2026-27825 protects download destinations but does not constrain source paths used by attachment uploads.
The OAuth fallback token directory and JSON file are created without explicit owner-only modes.