CVE-2026-27825 in mcp-atlassian
Summary
by MITRE • 03/10/2026
MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to version 0.17.0, the `confluence_download_attachment` MCP tool accepts a `download_path` parameter that is written to without any directory boundary enforcement. An attacker who can call this tool and supply or access a Confluence attachment with malicious content can write arbitrary content to any path the server process has write access to. Because the attacker controls both the write destination and the written content (via an uploaded Confluence attachment), this constitutes for arbitrary code execution (for example, writing a valid cron entry to `/etc/cron.d/` achieves code execution within one scheduler cycle with no server restart required). Version 0.17.0 fixes the issue.
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Analysis
by VulDB Data Team • 03/16/2026
The vulnerability described in CVE-2026-27825 represents a critical directory traversal flaw within the Model Context Protocol (MCP) server implementation for Atlassian products. This issue specifically affects the `confluence_download_attachment` tool which lacks proper input validation and sanitization mechanisms. The flaw exists in versions prior to 017.0 and demonstrates a classic path traversal vulnerability that allows attackers to manipulate file system write operations through improperly validated user-supplied parameters. The MCP server acts as an intermediary between AI models and Atlassian applications, enabling automated workflows and content processing, making this vulnerability particularly dangerous in environments where such integrations are utilized.
The technical implementation of this vulnerability stems from the absence of directory boundary enforcement when processing the `download_path` parameter within the attachment download functionality. When an attacker uploads a malicious Confluence attachment and subsequently invokes the vulnerable tool, the server processes the user-controlled path without validating whether it remains within the intended directory boundaries. This design flaw directly violates security principles outlined in CWE-22, which addresses improper limitation of a pathname to a restricted directory. The vulnerability enables attackers to write arbitrary content to any location accessible by the server process, effectively bypassing normal file system access controls and permissions.
The operational impact of this vulnerability extends far beyond simple unauthorized file writes, as it provides a pathway for full system compromise through arbitrary code execution. Attackers can leverage this vulnerability to establish persistent access by creating malicious cron jobs, writing backdoor scripts, or modifying system configuration files. The specific example of writing to `/etc/cron.d/` demonstrates how an attacker could execute code within a single scheduler cycle without requiring server restarts or additional privileges. This capability aligns with ATT&CK technique T1059.007 for command and script injection, and T1078 for valid accounts, as it allows for stealthy execution of malicious payloads. The vulnerability's exploitation potential increases significantly in environments where the MCP server process runs with elevated privileges or has access to sensitive system directories.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security hardening measures. Organizations should immediately upgrade to version 0.17.0 or later, which implements proper directory boundary enforcement for the `download_path` parameter. Additional defensive measures include implementing strict input validation for all user-supplied parameters, employing path normalization techniques, and establishing principle of least privilege access controls for the MCP server process. Network segmentation and monitoring of MCP server communications can help detect anomalous behavior indicative of exploitation attempts. The fix implemented in version 0.17.0 likely includes proper validation of file paths through absolute path resolution and comparison against allowed directories, preventing the traversal beyond intended boundaries. Security teams should also conduct thorough audits of all MCP tool implementations to identify similar vulnerabilities in other tools and establish comprehensive logging and alerting mechanisms for file system write operations originating from automated processes.