CVE-2026-77258: MCP Atlassian: Arbitrary file read/exfiltration via upload_attachment missing validate_safe_path()

In confluence/attachments.py, the two download methods call validate_safe_path() before writing (around lines 223 and 272). The upload method, lines 62 to 79, does not. It converts a relative path to absolute, checks os.path.exists(), takes the basename and calls _upload_attachment_direct(). The validator is already imported in that file; it was just never added to this path.

An MCP call such as confluence_upload_attachment with file_path set to /etc/passwd reads the file and attaches it to the chosen page. The reporter confirmed on mcp-atlassian 0.21.1 that the upload source contains no validator call while the download methods do.

The attacker needs the ability to call the tool: a connected agent, another MCP client, or a prompt injection that steers the agent. The attacker also needs a page to attach to. What leaves the machine is any file the server process can read, such as SSH keys, AWS credentials, .env files and application secrets. It lands on a Confluence instance that other users can open.

mcp-atlassian below 0.22.0 with the Confluence tools enabled. Jira-only setups are covered by the sibling advisories.

pip show mcp-atlassian

If you launch it with uvx or from a container image, read the pinned version in your MCP client config or compose file.

Upgrade to 0.22.0:

pip install --upgrade mcp-atlassian==0.22.0

The reporter's suggested fix was to call validate_safe_path(file_path) before the existence check in upload_attachment, matching the download methods. The fix ships in pull request 1448. The advisory lists no workaround.

Check Confluence pages for attachments uploaded by the MCP service account that you do not recognise, particularly files named after credentials, keys or environment dumps. Page history and the Confluence audit log show who attached what and when. In MCP logs, search for confluence_upload_attachment calls with an absolute file_path outside your intended upload directory. Beam's record of agent MCP tool calls can tie such a call to an agent session.

Summary

The upload_attachment method in confluence/attachments.py reads and uploads arbitrary local files to Confluence without calling validate_safe_path(). Both download methods (download_attachment at line 223, download_content_attachments at line 272) correctly call validate_safe_path() before writing files, but the upload path at lines 35-79 skips this check entirely.

An AI agent connected via MCP (or an attacker influencing that agent through prompt injection) can read any file on the host and exfiltrate it by uploading it as a Confluence page attachment.

Vulnerable Code

File: src/mcp_atlassian/confluence/attachments.py, lines 62-79

# No validate_safe_path() call anywhere in this method
if not os.path.isabs(file_path):
    file_path = os.path.abspath(file_path)

if not os.path.exists(file_path):
    return {"success": False, "error": f"File not found: {file_path}"}

filename = os.path.basename(file_path)
attachment = self._upload_attachment_direct(
    content_id, file_path, filename, comment, minor_edit
)

The validate_safe_path function is already imported at line 9 of the same file, and used in the download methods. It was just not added to the upload path.

Proof of Concept

Tested with mcp-atlassian 0.21.1 on Python 3.11 (EC2, Amazon Linux 2023).

import inspect
from mcp_atlassian.confluence.attachments import AttachmentsMixin

# Confirm: no validate_safe_path in upload
source = inspect.getsource(AttachmentsMixin.upload_attachment)
assert "validate_safe_path" not in source  # passes

# Confirm: validate_safe_path IS in downloads
assert "validate_safe_path" in inspect.getsource(AttachmentsMixin.download_attachment)  # passes
assert "validate_safe_path" in inspect.getsource(AttachmentsMixin.download_content_attachments)  # passes

An MCP tool call like this reads /etc/passwd and uploads it to Confluence:

{"tool": "confluence_upload_attachment", "arguments": {"content_id": "123456", "file_path": "/etc/passwd"}}

Impact

Exfiltration of any file readable by the MCP server process: SSH keys, AWS credentials, .env files, /etc/passwd, application secrets. Data leaves the local machine and lands on a remote Confluence instance accessible to other users.

Suggested Fix

Add validate_safe_path(file_path) before the os.path.exists() check in upload_attachment, matching the existing pattern in the download methods. The function is already imported.