CVE-2026-77258 in mcp-atlassian
Summary
by MITRE • 09/22/2026
MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, upload_attachment in src/mcp_atlassian/confluence/attachments.py accepts a caller-controlled file_path and opens the selected server-local file without restricting it to the workspace. A permitted Confluence MCP caller can upload the file as an attachment and disclose data readable by the server process. This issue is fixed in version 0.22.0.
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Analysis
by VulDB Data Team • 09/22/2026
The vulnerability identified in MCP Atlassian prior to version 0.22.0 represents a critical path traversal and unauthorized information disclosure flaw within the Model Context Protocol implementation for Atlassian products such as Confluence and Jira. The core of this issue resides in the upload_attachment function located in the src/mcp_atlassian/confluence/attachments.py module. This component is responsible for handling file uploads from clients interacting with the MCP server, a protocol designed to standardize how large language models interact with external tools and data sources. In versions preceding 0.22.0, the implementation failed to adequately sanitize or validate the file_path parameter provided by the caller. Instead of restricting access strictly to designated workspace directories or allowing only specific content types within controlled boundaries, the server directly utilized the user-supplied path to open files on the underlying operating system. This lack of input validation allowed an attacker with permission to invoke this MCP endpoint to specify arbitrary absolute paths on the server's file system.
From a technical perspective, this flaw constitutes a classic Path Traversal vulnerability, often categorized under CWE-22: Improper Limitation of a Pathname to a Restricted Directory. By supplying maliciously crafted path strings that include directory traversal sequences or direct references to sensitive locations such as /etc/passwd on Linux systems or configuration files containing API keys and credentials on Windows servers, an authenticated caller could force the server process to read and subsequently upload arbitrary local files as attachments within Confluence pages. The operational impact is severe because it bypasses standard access controls associated with the Atlassian application itself. Even if a user does not have direct file system permissions or administrative rights within Jira or Confluence, their ability to interact with the MCP server grants them an indirect vector to exfiltrate sensitive data stored on the host machine where the MCP server is running. This effectively transforms a routine feature into a powerful information disclosure tool, potentially leading to further compromise if combined with other vulnerabilities such as Server-Side Request Forgery or remote code execution attempts that rely on uploaded files for payload delivery.
The security implications extend beyond simple data leakage. The ability to read arbitrary files can facilitate the extraction of environment variables, private keys, database connection strings, and internal network configurations. This aligns closely with ATT&CK technique T1083: File and Directory Discovery, as well as T1530: Data from Local System, which describe adversary behaviors focused on gathering information about a compromised system to support further operations. The vulnerability highlights the risks inherent in exposing server-side capabilities through API endpoints without rigorous boundary checks, particularly when those APIs are designed for integration with AI models that may not inherently understand security constraints of the underlying infrastructure.
To mitigate this risk, organizations must immediately upgrade MCP Atlassian to version 0.22.0 or later, where the developers have implemented proper path validation and restriction mechanisms. This fix ensures that file operations are confined strictly within allowed workspace directories, preventing access to parent directories or unrelated system files. In addition to upgrading, administrators should enforce strict least-privilege principles for the user accounts interacting with the MCP server, ensuring that only trusted entities can invoke attachment-related functions. Network-level controls such as firewalls and API gateways should also be configured to restrict access to these endpoints based on IP reputation and authentication status. Regular security audits of custom integrations and third-party plugins are essential to identify similar path handling flaws before they can be exploited in production environments.