mcp-atlassian authentication bypass vulnerability CVE-2026-77244

The community MCP server mcp-atlassian was disclosed to have an authentication bypass vulnerability CVE-2026-77244 with a CVSS score of 10.0. Anyone able to access its HTTP service can use the deployer's Atlassian credentials to operate Jira and Confluence without an account or token. The vulnerability stems from the token validator accepting any non-empty string, OAuth proxy not being enabled by default, middleware not rejecting missing Authorization headers, and data-fetching logic falling back to operator credentials in environment variables, giving attackers read and write access to all projects, issues, comments, and pages available to that account, with audit logs recording only the operator. The fix was provided in version 0.22.0 released on July 10, 2026, changing the global credential fallback to ALLOW_GLOBAL_CRED_FALLBACK, which is disabled by default; however, the same bypass in the SSE transport path was not fixed until version 0.23.1 on August 19, and versions 0.23.0 and earlier remain affected.