CVE-2026-77274

Name of the Vulnerable Software and Affected Versions MCP Atlassian versions prior to 0.22.0

Description A backslash authority confusion exists in the header-based Jira and Confluence URL authentication flow. The validate url for ssrf() function interprets the authority of a URL differently than the Requests connection layer. By using a crafted URL containing a backslash before userinfo-like syntax, an attacker can bypass SSRF (Server-Side Request Forgery) protections. In this scenario, the validation function identifies an external hostname as the target, while the HTTP client connects to an internal host, allowing unauthorized server-side requests to protected network resources, such as loopback or internal services. This issue can be triggered via the POST /mcp endpoint by providing a malicious URL in the X-Atlassian-Jira-Url or X-Atlassian-Confluence-Url headers.

Recommendations Update MCP Atlassian to version 0.22.0. As a temporary mitigation, restrict or validate the input provided to the X-Atlassian-Jira-Url and X-Atlassian-Confluence-Url headers to prevent the use of backslashes in the authority section of the URL.