CVE-2026-77269 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 remediation for CVE-2026-27825 protects download destinations but does not constrain source paths used by attachment uploads. A caller can provide an absolute or traversal file_path and cause the server to upload the selected local file. The advisory traces the vulnerable input and processing flow through upload_attachment, file_path, and CVE-2026-27825, 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 as CVE-2026-27825 within MCP Atlassian versions prior to 0.22.0 represents a critical path traversal flaw that undermines the integrity of file upload operations. This security issue stems from an incomplete remediation strategy implemented in earlier patches, which focused exclusively on restricting download destinations while neglecting equivalent controls for source paths during attachment uploads. The Model Context Protocol server, designed to interface with Atlassian products such as Confluence and Jira, processes user-supplied input without sufficient validation when handling file upload requests. This oversight allows an attacker to manipulate the file_path parameter by providing absolute paths or directory traversal sequences, thereby bypassing intended security boundaries that are meant to confine operations within designated directories.
From a technical perspective, the flaw resides in the upload_attachment function and its interaction with the underlying file system APIs. When a caller submits a request containing a maliciously crafted file path, the server fails to sanitize or validate this input against a whitelist of allowed source locations. Instead of restricting uploads to specific whitelisted directories, the application trusts the provided path directly. This lack of constraint enables the selection of arbitrary local files on the host system where the MCP Atlassian service is running. The vulnerability exploits the asymmetry in security controls between read and write operations, highlighting a common pitfall in web server development where download restrictions are rigorously enforced while upload source validation is overlooked or inadequately implemented.
The operational impact of this vulnerability is severe, as it effectively grants an authenticated attacker the ability to exfiltrate sensitive data from the host machine. By uploading arbitrary local files through the application interface, an adversary can read and transmit contents of configuration files, private keys, database credentials, or other confidential information stored on the server's file system. This capability transforms a standard file upload feature into a powerful remote code execution precursor or data theft vector, depending on how the uploaded content is subsequently processed by downstream Atlassian services. The breach compromises confidentiality and potentially integrity if the uploaded files are used to overwrite existing critical configurations or scripts within the application environment.
This vulnerability aligns with CWE-22: Improper Limitation of a Pathname to a Restricted Directory, specifically in the context of source file selection rather than destination restriction. It also maps to MITRE ATT&CK techniques related to Data from Local System Retrieval and potentially Command and Control if used for staging malicious payloads. The failure to implement consistent input validation across both read and write operations illustrates a gap in secure coding practices that assumes prior remediation efforts were comprehensive when they were only partially applied.
To mitigate this risk, organizations must immediately upgrade MCP Atlassian to version 0.22.0 or later, where the developers have addressed the asymmetry by enforcing strict constraints on source paths during upload operations. In addition to upgrading, administrators should implement defense-in-depth strategies such as running the service with minimal file system permissions using principle of least privilege, ensuring that the application user account cannot access sensitive directories outside its designated working area. Network-level controls and web application firewalls can also be configured to detect and block requests containing path traversal patterns or absolute paths in upload parameters, providing an additional layer of protection while patching efforts are completed. Regular security audits should verify that all file handling functions enforce bidirectional validation for both source and destination paths to prevent similar oversights in future updates.