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CVE-2026-77248 – Unauthenticated Arbitrary File Read via Path Traversal – mcp-atlassian < 0.22.0

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Summary

CVE-2026-77248 is a critical, chained vulnerability in mcp-atlassian, a Model Context Protocol (MCP) server that connects AI agents to Jira and Confluence. Versions prior to 0.22.0 allow an unauthenticated network attacker to combine a missing-authentication flaw in the streamable-HTTP transport with a path traversal flaw in the upload_attachment tool to read arbitrary files accessible to the MCP server process — including operator Atlassian API tokens and other secrets. The issue carries a CVSS v3.1 base score of 8.6 (High).

Technical details

  • Root cause 1 (Missing authentication, CWE-306): The streamable-HTTP transport does not require an Authorization header on incoming requests. When no token is supplied, requests fall through and are processed using the operator’s globally configured Atlassian credentials rather than being rejected.
  • Root cause 2 (Path traversal, CWE-22/CWE-73): The upload_attachment tool’s file_path parameter is passed directly to a file open() call without sanitization or confinement to a safe workspace directory, unlike the server’s hardened download path.
  • Attack vector: Network — no privileges and no user interaction are required (AV:N/AC:L/PR:N/UI:N).
  • Trigger conditions: The mcp-atlassian server is deployed with the streamable-HTTP transport reachable over the network, and an attacker sends an unauthenticated upload_attachment (or equivalent attachment-upload) tool call with an arbitrary/absolute or traversal-style file_path (e.g., /proc/self/environ).
  • Impact: High confidentiality impact — the attacker can read arbitrary files readable by the server process (configuration files, environment variables, credential material) and exfiltrate them by having them uploaded as an attachment to an attacker-reachable Jira or Confluence item. No direct integrity or availability impact is asserted (S:C/C:H/I:N/A:N).

Affected software

  • sooperset/mcp-atlassian, all versions prior to 0.22.0
  • Fixed in mcp-atlassian 0.22.0

Severity

  • CVSS v3.1 Base Score: 8.6 (High)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

Mitigation and recommended actions

  • Immediate: Upgrade mcp-atlassian to version 0.22.0 or later, which enforces authentication at the transport boundary (unauthenticated streamable-HTTP requests are now rejected with a 401 by default instead of falling back to operator credentials) and validates all attachment/content file paths against the server’s working directory via validate_safe_path.
  • If immediate patching is not possible:
    • Restrict network exposure of the mcp-atlassian streamable-HTTP endpoint to trusted hosts only (e.g., via firewall rules, VPN, or internal-only network placement) until the upgrade can be applied.
    • Ensure any global credential fallback behavior is explicitly disabled and not relied upon in production deployments.
    • Monitor for anomalous upload_attachment calls containing absolute paths or path-traversal sequences (e.g., ../, /proc/, /etc/) in server logs.

References

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