CVE-2026-77248 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, the streamable HTTP transport accepts requests without a user identity and falls back to operator credentials, while upload_attachment accepts an unrestricted file_path. An unauthenticated network caller can read files available to the MCP process, upload them to an attacker-selected Jira issue or Confluence page, and retrieve the contents. The advisory traces the vulnerable input and processing flow through streamable-http, UserTokenMiddleware, upload_attachment, file_path, and _get_fetcher, which identify the affected entry points, controls, and code paths. 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 versions prior to 0.22.0 represents a critical failure in authentication enforcement and input validation within the Model Context Protocol server implementation for Atlassian products such as Confluence and Jira. This security flaw stems from two distinct but related issues: an improper handling of user identity during streamable HTTP transport requests and insufficient sanitization of file paths provided to the upload_attachment function. The architecture relies on a middleware component known as UserTokenMiddleware, which is designed to associate incoming requests with specific user identities. However, in versions prior to 0.22.0, this middleware fails to enforce identity requirements for certain request types, allowing unauthenticated network callers to bypass authentication checks entirely. When no valid user token or identity is provided, the system defaults to using operator credentials rather than rejecting the request outright. This fallback mechanism effectively grants attackers access with elevated privileges associated with the service account running the MCP process, thereby circumventing standard role-based access controls inherent in Atlassian platforms.
The second aspect of this vulnerability involves the upload_attachment functionality, which accepts a file_path parameter without adequate validation or restriction. An attacker can supply arbitrary file paths that are accessible to the operating system user under which the MCP server operates. This lack of input sanitization allows for both local file read and write operations beyond intended boundaries. By exploiting unrestricted file path handling, an unauthenticated actor can read sensitive files from the host environment where the MCP process resides. These files may contain configuration data, secrets, or other proprietary information that is not meant to be exposed through the API interface. Furthermore, the ability to specify arbitrary destinations for uploads enables the attacker to exfiltrate these retrieved file contents by uploading them directly into a Jira issue or Confluence page controlled by the attacker. This creates a covert channel for data theft, as the uploaded content becomes visible within the Atlassian workspace, potentially accessible to other users depending on the permissions of the target ticket or page.
The operational impact of this vulnerability is severe due to its unauthenticated nature and the breadth of access it provides. Since no authentication is required to trigger these flaws, any network-accessible client can exploit the issue without prior credentials. The combination of reading arbitrary files from the server environment and writing them into Atlassian applications results in a significant confidentiality breach. Attackers can extract sensitive configuration files, source code, database connection strings, or internal documentation stored on the host machine. Additionally, by uploading malicious content to Jira issues or Confluence pages, attackers could potentially facilitate further attacks such as social engineering campaigns against other employees who view these items, or even attempt remote code execution if specific file types are processed server-side upon upload. The vulnerability affects core entry points including streamable-http transport handling and the _get_fetcher logic that processes file operations, indicating a systemic weakness in how external inputs are validated before interacting with system resources.
This issue aligns with CWE-287 Improper Authentication, as the system fails to properly verify identity for certain requests, defaulting instead to privileged operator credentials. It also corresponds to CWE-22 Path Traversal: ../ 'directory traversal' or similar constructs in file_path parameters, reflecting the lack of validation on user-supplied paths that determine which files are accessed. From an ATT&CK perspective, this vulnerability facilitates Data from Local System (T1005) through unauthorized file reads and potentially Command and Control via uploaded content if used for beaconing or data staging within the Atlassian workspace. The exploitation chain involves leveraging unauthenticated access to bypass security controls, followed by arbitrary file read operations to gather intelligence, and finally using the application's own features to exfiltrate that data into a persistent location under attacker control.
Mitigation strategies primarily involve upgrading MCP Atlassian to version 0.22.0 or later, where these flaws have been addressed through stricter authentication enforcement in UserTokenMiddleware and enhanced validation of file_path inputs within upload_attachment. Until the upgrade is performed, organizations should restrict network access to the MCP server endpoint using firewall rules or reverse proxy configurations that require valid API tokens for all requests. Implementing strict allow-lists for permitted file paths can also reduce risk by limiting which files are accessible via the application interface. Additionally, monitoring logs for unusual upload activities or unexpected file accesses may help detect exploitation attempts in real-time. Ensuring that the MCP process runs with minimal necessary privileges further limits the potential damage if an attacker manages to read local files, as they will only have access to resources permitted by that restricted user account rather than full operator-level permissions.