CVE-2026-77256
Received Received - Intake

MCP Atlassian OAuth Token Exposure via Umask Misconfiguration

Publication date: 2026-09-22

Last updated on: 2026-09-22

Assigner: GitHub, Inc.

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.

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Meta Information

Published
2026-09-22
Last Modified
2026-09-22
Generated
2026-09-22
AI Q&A
2026-09-22
EPSS Evaluated
N/A
NVD
CVE-2026-77256
EUVD
EUVD-2026-84761

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
atlassian mcp_atlassian 0.22.0
atlassian mcp 0.22.0

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-732 The product specifies permissions for a security-critical resource in a way that allows that resource to be read or modified by unintended actors.

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Executive Summary

CVE-2026-77256 affects MCP Atlassian, a Model Context Protocol server for Confluence and Jira. It involves a plaintext OAuth fallback file storing refresh and access tokens being written with weak permissions due to the process umask. Local users with access to the system can read this file and gain unauthorized access to Atlassian resources using the tokens.

Detection Guidance

Check for world-readable OAuth token backup files in the mcp-atlassian configuration directory. Look for files like refresh_token or access_token in ~/.config/mcp-atlassian/ or /tmp/. Use commands like 'find ~/.config/mcp-atlassian/ -type f -perm -o=r' to detect files readable by others. Verify directory permissions with 'ls -ld ~/.config/mcp-atlassian/'.

Impact Analysis

If you use MCP Atlassian versions before 0.22.0, attackers with local access to your system could read the OAuth token backup file. This allows them to access your Jira or Confluence accounts without needing your password or browser session, potentially leading to data theft or unauthorized actions in your Atlassian projects.

Compliance Impact

This vulnerability could violate compliance requirements that mandate strict access controls for sensitive data. Unauthorized local access to OAuth tokens may expose protected user data, leading to potential breaches of GDPR, HIPAA, or other regulations requiring data confidentiality and controlled access.

Mitigation Strategies

Upgrade mcp-atlassian to version 0.22.0 or later. If upgrading is not possible, manually set restrictive permissions on the OAuth token directory and files using 'chmod 700 ~/.config/mcp-atlassian/' and 'chmod 600 ~/.config/mcp-atlassian/refresh_token'. Remove any existing world-readable token files.

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