The MCP Atlassian server prior to version 0.22.0 processes the X-Atlassian-Jira-Url and X-Atlassian-Confluence-Url headers in the _process_authentication_headers function without invoking the validate_url_for_ssrf function. This omission allows an attacker capable of setting these headers to supply URLs pointing to internal or metadata services, causing the server to make unintended requests to those destinations. This SSRF vulnerability bypasses the incomplete remediation applied for CVE-2026-27826. The issue is resolved in version 0.22.0 by properly validating these URLs.

An attacker with the ability to set the specified headers can exploit this vulnerability to make the MCP Atlassian server send requests to internal network resources or metadata services. This can lead to unauthorized access to internal services or sensitive information exposure. The CVSS 4.0 score is 8.3 (high severity), indicating a network attack vector with low complexity and no required privileges or user interaction, but with high confidentiality impact.

Upgrade MCP Atlassian to version 0.22.0 or later, where this SSRF vulnerability is fixed by proper URL validation. No other mitigation is indicated or required according to the vendor advisory. Patch status is confirmed fixed in 0.22.0.