The MCP Atlassian server writes a plaintext fallback file that contains OAuth refresh and access tokens. The file is created with permissions that inherit the process umask, so under common or permissive settings the file becomes world‑readable. This makes it possible for any local user to read the backup file and use the refresh token to obtain continued access to Atlassian services. The weakness is an insecure file‑permission issue (CWE‑732).

The vulnerability affects the sooperset MCP Atlassian product, a Model Context Protocol server used to support Atlassian Confluence and Jira. Versions prior to 0.22.0 are impacted; the issue is fixed in 0.22.0 and later.

The CVSS score of 8.3 indicates a high severity vulnerability. No EPSS score is available, and the vulnerability is not listed in CISA’s KEV catalog. The attack vector is local: any user who can write to the directory where the backup file is stored can read it under default Unix umask settings. A local attacker who reads the file can use the refresh token to maintain access to the Atlassian instance, potentially bypassing authentication controls.