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CVE-2026-77244 – Critical Authentication Bypass / Full Jira & Confluence Takeover – mcp-atlassian <

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Summary

CVE-2026-77244 is a critical authentication bypass vulnerability (CVSS 3.1 score: 10.0) in mcp-atlassian, an open-source Model Context Protocol (MCP) server that connects AI assistants to Jira and Confluence. When deployed over HTTP transport, the server’s AtlassianOpaqueTokenVerifier accepts any non-empty string as a valid authentication token and, absent a legitimate user token, silently falls back to the operator’s own configured Atlassian credentials — granting any network-reachable client full, unauthenticated operator-level access to Jira and Confluence.

Technical details

  • Root cause: Three converging design flaws — (1) AtlassianOpaqueTokenVerifier.verify_token() treats any non-empty string as valid without cryptographic verification, introspection, or format checking; (2) when OAuth proxy authentication is disabled (the default configuration), the HTTP transport accepts requests without challenging for credentials; (3) when no valid user-supplied token is present, the server falls back to environment-configured credentials (e.g., JIRA_API_TOKEN, JIRA_USERNAME) rather than rejecting the request.
  • Trigger conditions: The MCP server is running with streamable-HTTP transport enabled and is reachable over the network, with OAuth proxy authentication left at its default (disabled) state.
  • Attack vector: Network (AV:N), no privileges or user interaction required. An attacker sends a request to the MCP HTTP endpoint with either no Authorization header or an arbitrary/garbage Bearer token; the request still reaches tool handlers and executes using the operator’s credentials.
  • Impact: Complete compromise of confidentiality and integrity of connected Jira and Confluence data — full read/write access to issues, pages, and attachments, actions performed and audited under the operator’s identity, ability to create persistent webhooks/automation rules, and potential exposure of sensitive credentials stored in linked document repositories. Availability is not impacted (A:N).

Affected software

  • mcp-atlassian (vendor: sooperset) versions prior to 0.22.0, when deployed with streamable-HTTP transport
  • Fixed in version 0.22.0 and later

Severity

  • CVSS v3.1 Base Score: 10.0 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

Mitigation and recommended actions

  • Immediate: Upgrade mcp-atlassian to version 0.22.0 or later, which rejects unauthenticated HTTP requests with a 401 response at the transport boundary and gates any credential fallback behind an explicit opt-in flag (ALLOW_GLOBAL_CRED_FALLBACK, disabled by default).
  • If immediate patching is not possible:
    • Do not expose the MCP HTTP transport directly to untrusted networks; bind it to 127.0.0.1 or restrict access via firewall/VPN to trusted hosts only.
    • Disable global credential fallback and require OAuth-based authentication for all HTTP transport deployments.
    • Audit Jira/Confluence activity logs for unexpected actions performed under the operator/service account identity.
    • Rotate the operator’s Atlassian API credentials configured for the MCP server if exposure is suspected.

References

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