CVE-2026-77267 in mcp-atlassian
Summary
by MITRE • 09/22/2026
MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the X-Atlassian-Jira-Url and X-Atlassian-Confluence-Url headers are processed by _process_authentication_headers and used to construct Atlassian fetchers without calling validate_url_for_ssrf. A caller who can set these headers can supply an internal or metadata-service URL and cause the server to send requests to that destination, bypassing the incomplete CVE-2026-27826 remediation. This issue is fixed in version 0.22.0.
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Analysis
by VulDB Data Team • 09/22/2026
The vulnerability identified in MCP Atlassian versions prior to 0.22.0 represents a critical Server-Side Request Forgery (SSRF) flaw rooted in improper input validation of HTTP headers. The Model Context Protocol server, designed to interface with Atlassian products such as Confluence and Jira, processes specific custom headers named X-Atlassian-Jira-Url and X-Atlassian-Confluence-Url within the _process_authentication_headers function. These headers are intended to direct internal routing or authentication flows but were inadvertently used to construct URL fetchers without undergoing necessary security checks. Specifically, the code path fails to invoke validate_url_for_ssrf before utilizing these header values to initiate network requests. This omission allows an attacker who can inject or manipulate these HTTP headers to dictate arbitrary destinations for server-side requests.
The operational impact of this flaw is severe due to its potential for internal network reconnaissance and data exfiltration. By supplying a maliciously crafted URL in the specified headers, an authenticated user or an attacker with access to modify request metadata can force the MCP Atlassian server to send HTTP requests to internal services that are not exposed to the public internet. This includes accessing cloud provider metadata endpoints, such as AWS EC2 instance metadata service, which often contain sensitive credentials and configuration data. Furthermore, attackers could target internal microservices, databases, or administrative interfaces within the organization's network perimeter. The vulnerability effectively bypasses existing security controls intended to mitigate SSRF attacks, rendering previous remediation efforts for related issues like CVE-2026-27826 ineffective against this specific attack vector involving header manipulation.
From a classification perspective, this issue aligns with CWE-918 Server-Side Request Forgery (SSRF), specifically falling under the sub-category of SSRF via HTTP headers where user-controlled input is used to construct URLs without proper validation. In terms of adversary tactics, this vulnerability facilitates techniques associated with ATT&CK T1557 Adversary-in-the-Middle or T1046 Network Service Discovery, as it allows an attacker to probe internal network services and potentially intercept communications between the MCP server and backend Atlassian instances. The lack of URL validation means that standard allow-listing or block-listing mechanisms typically employed in SSRF mitigations are circumvented because the input is not sanitized before being passed to the underlying HTTP client library.
To mitigate this vulnerability, organizations must immediately upgrade MCP Atlassian to version 0.22.0 or later, where the developers have implemented proper URL validation for these headers. In environments where upgrading is not immediately feasible, network-level controls such as firewall rules should be configured to restrict outbound connections from the server hosting the MCP instance. These restrictions should block access to known internal IP ranges and cloud metadata endpoints while allowing only necessary external traffic. Additionally, implementing strict input validation at the API gateway or reverse proxy level can help filter out malformed headers before they reach the application logic. Security teams should also audit logs for unusual patterns in X-Atlassian-Jira-Url and X-Atlassian-Confluence-Url header values to detect potential exploitation attempts during the transition period.