CVE-2026-77250
MCP Atlassian: OAuth fallback token storage writes plaintext access and refresh tokens with group-readable permissions
MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, OAuthConfig writes a plaintext fallback file containing access and refresh tokens under the user's .mcp-atlassian directory using process-default permissions. On systems with a permissive umask, same-group or other local users and processes can read the persisted tokens and reuse the associated Atlassian access. The advisory traces the vulnerable input and processing flow through OAuthConfig._save_tokens, ~/.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.
- Affected
- sooperset · mcp-atlassian
- CVSS v3.1 GITHUB
- 6.1 MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N - EPSS
- 0.11% chance of exploitation in the next 30 days, 1st percentile
- Published
- 2026-09-22