Executive brief
MCP Atlassian stores OAuth tokens (access and refresh credentials) in a plaintext file in the user's home directory with world-readable permissions. Any user or process on the same system with access to the home directory can steal these tokens and impersonate the account to Atlassian APIs, enabling account compromise and unauthorized access to Atlassian services.
Technical details
The vulnerability exists in the OAuthConfig._save_tokens() method, which writes OAuth tokens (access_token and refresh_token) to ~/.mcp-atlassian/oauth-<client_id>.json with default umask permissions (mode 0o664) instead of restrictive owner-only permissions (0o600). The fallback file is created unconditionally for backwards compatibility even when keyring storage succeeds, and no chmod or secure open mode is applied. An attacker with local filesystem access can read this file, extract the tokens, and use the refresh token to maintain persistent access to the victim's Atlassian account. The vulnerability affects shared systems, containers, developer workstations, and CI runners.
Affected products
- Atlassian MCP Atlassian <UNKNOWN>
Timeline
- 2026-09-22: disclosed