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CVE-2026-77256

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

CVSS 4.0 8.3 HIGHCheck source for fixed versionsKEV status unknown

Original advisory

cve-program · CVE-2026-77256

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-77256

Published

mcp-atlassian

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "sooperset",
                    "product": "mcp-atlassian",
                    "versions": [
                        {
                            "version": "< 0.22.0",
                            "status": "affected"
                        }
                    ]
                }

Original source record · Cite this exact observation · Complete original publisher JSON