What’s Vulnerable › Vulnerabilities

CVE-2026-77256: MCP Atlassian: OAuth refresh-token backup file is world-readable under default Unix umask

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-22 · updated 2026-09-28
• Weakness: CWE-732

Description

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the plaintext OAuth fallback file containing refresh and access tokens is written with permissions inherited from the process umask. Under common or permissive configurations, other local users can read the backup and retain Atlassian access through the refresh token. The advisory traces the vulnerable input and processing flow through OAuthConfig._save_tokens_to_file, refresh_token, access_token, and umask, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.

Affected products

• sooperset mcp-atlassian: before 0.22.0 — fixed in 0.22.0

How to fix

Upgrade to a fixed version: sooperset mcp-atlassian 0.22.0. Check the vendor advisory for mitigations.

References

• https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460
• https://github.com/sooperset/mcp-atlassian/pull/1448
• https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0
• https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-76pr-5669-3xf5
• https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-76pr-5669-3xf5

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