CVE-2026-77268 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 OAuth fallback token directory and JSON file are created without explicit owner-only modes. Local users or processes with access through the resulting group or world permission bits can read access and refresh tokens and reuse the associated Atlassian session. The advisory traces the vulnerable input and processing flow through ~/.mcp-atlassian, oauth-<client_id>.json, access_token, and refresh_token, 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 prior to version 0.22.0 represents a critical misconfiguration of file system permissions that leads to unauthorized access to sensitive authentication credentials. As a Model Context Protocol server designed for integration with Atlassian products such as Confluence and Jira, the application handles OAuth flows to authenticate users and manage sessions securely. However, during the initialization or storage phase of these tokens, the software fails to enforce restrictive file system modes on the directory structure located at ~/.mcp-atlassian and specifically within the oauth-<client_id>.json files that store access_token and refresh_token values. This oversight results in the creation of directories and files with overly permissive group or world read permissions rather than owner-only restrictions, thereby exposing sensitive data to any local user or process on the same system account where the server is executed.
From a technical perspective, this flaw constitutes an improper file permission setting that allows unintended information disclosure. The operational impact is severe because access tokens and refresh tokens are essentially keys to the victim's Atlassian session. An attacker with local access to the machine can read these JSON files without needing valid credentials for the application itself. By extracting the stored tokens, the adversary can reuse them to authenticate as the legitimate user against Atlassian services. This effectively bypasses multi-factor authentication and other security controls that rely on initial login verification, granting the attacker full administrative or user-level access depending on the victim's privileges within Confluence or Jira. The vulnerability is particularly dangerous in shared hosting environments, virtual machines, or development workstations where multiple users may have shell access to the same account, as it requires no remote exploitation vector and relies solely on local privilege escalation through file system traversal.
This issue aligns with CWE-732, which describes improper permission assignment for critical resources, specifically regarding the failure to restrict permissions to authorized entities only. Furthermore, in the context of the MITRE ATT&CK framework, this vulnerability facilitates Initial Access via Valid Accounts and Credential Access techniques such as Unsecured Credentials or Stored Credentials. The attack path involves local enumeration followed by credential harvesting, allowing an adversary to pivot from a low-privilege shell session into high-value enterprise applications without triggering typical intrusion detection alerts associated with brute force or password spraying attacks.
To mitigate this vulnerability, organizations must upgrade MCP Atlassian to version 0.22.0 or later, where the developers have implemented explicit owner-only modes for the token directory and JSON files. Until an update is applied, administrators should manually enforce restrictive permissions on the ~/.mcp-atlassian directory and its contents using standard operating system commands such as chmod 700 for directories and chmod 600 for files to ensure that only the file owner can read or write them. Additionally, it is advisable to rotate any potentially exposed tokens immediately if there is suspicion of compromise, revoke existing sessions in Atlassian products, and audit local user accounts on systems running this software to identify potential unauthorized access attempts. Regular security audits focusing on configuration management and permission hygiene are essential to prevent similar misconfigurations in other components that handle sensitive state data locally.