Summary
MCP Atlassian's attachment upload function can accept a file path controlled by an attacker without consistently enforcing workspace boundaries. A caller who can invoke this function may cause server-readable files outside the intended workspace to be uploaded to Confluence.
Affected context
The vulnerability occurs in deployments of the MCP Atlassian server where:
- The Confluence attachment upload tool is enabled
- Callers can supply the
file_pathargument - The server process can read files outside its designated workspace
- Path validation does not consistently restrict file access to the intended directory
The risk depends on the permissions of the MCP caller and the files readable by the server account.
Exploit preconditions
- Attack surface: The
confluence_upload_attachmentMCP tool - Required access: Permission or ability to invoke the attachment upload operation
- Trigger point: Processing of the attacker-controlled
file_pathvalue - Why exploitation is possible: The upload flow permits traversal outside the workspace and reads the selected file before sending it to Confluence
Why this happens
The underlying issue is insufficient canonical path validation for a file operation that accepts attacker-controlled input. When a supplied path is resolved without enforcing that the resulting location remains within an approved workspace, directory traversal sequences can reference files outside the intended boundary. This maps to CWE-22: Improper Limitation of a Pathname to a Restricted Directory, commonly known as path traversal.
Potential impact
- Sensitive server-readable files may be uploaded to Confluence
- Credentials, configuration data, or source code could be exposed
- Confidentiality of the MCP server environment may be reduced
- Exfiltrated files could support follow-on attacks against connected systems
- Confluence content could become a repository for improperly disclosed data
General mitigation guidance
Mitigation generally focuses on enforcing a narrow, explicit file-access boundary for every upload operation.
Common defensive patterns include:
- Resolve and canonicalize paths before access
- Verify that the canonical path remains inside an approved workspace
- Prefer server-side file identifiers or constrained object references over raw paths
- Reject traversal markers, symbolic-link escapes, and ambiguous path formats
- Run the MCP server with least-privilege filesystem permissions
- Restrict which files and directories are readable by the service account
- Apply outbound controls and content policies to attachment uploads
These controls reduce the impact of path-validation failures and limit the data available to an attacker.
How teams detect issues like this
Organizations can look for path traversal risks through:
- Static analysis of file APIs receiving user-controlled path values
- Code review checks for canonicalization followed by directory-boundary validation
- Tests covering relative paths, encoded separators, absolute paths, and symbolic links
- Runtime monitoring for uploads whose source paths fall outside approved workspaces
- Policy enforcement requiring allowlisted directories and least-privilege service accounts
Automated security review tools may help identify path-construction and file-access patterns that bypass workspace restrictions.
