MCP Atlassian, a protocol server used to connect Atlassian products such as Confluence and Jira, creates OAuth fallback token files without owner‑only file permissions before version 0.22.0. This allows local users or processes that gain access through shared group or world permission bits to read the JSON file containing access and refresh tokens, thereby enabling them to reuse the associated Atlassian session and bypass authentication. The weakness is a file permission issue, identified as CWE-732.

Affected systems include installations of the MCP Atlassian server running any version earlier than 0.22.0. The vulnerability specifically relates to the default token storage location under ~/.mcp-atlassian, where the oauth-<client_id>.json file, access_token, and refresh_token entries are created. It impacts users who have local access to the underlying operating system where the server runs, including users with group or world permissions to the token directory.

The vulnerability has a CVSS score of 5.5, indicating moderate severity. No EPSS data is available, and the issue is not listed in CISA KEV catalogs. Attackers can exploit the weak permissions by simply reading the token files locally, reading the tokens and reusing the session. The vulnerability requires local access to the server system but does not require any network access or privileged escalation, so the likelihood of exploitation depends on the presence of local users with sufficient directory permissions.