CVE-2026-77274 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, validate_url_for_ssrf has a backslash authority confusion because it interprets the authority differently from the Requests connection layer in the header-based Jira and Confluence URL authentication flow. A crafted URL can validate as an external hostname while the HTTP client connects to an internal host, permitting server-side requests to protected network resources. 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 URL parsing inconsistencies within the authentication flow for Jira and Confluence integrations. The core technical defect lies in the validate_url_for_ssrf function, which fails to normalize or strictly parse URLs with backslash characters in the authority section of the URI scheme. Specifically, when a crafted URL containing a backslash is processed, the validation logic interprets the host component differently than the underlying HTTP client library used by the Requests connection layer. This discrepancy allows an attacker to construct a maliciously formatted URL that passes external hostname validation checks but results in the actual network request being directed toward internal or protected network resources.
This behavior exploits a well-known class of vulnerabilities categorized under CWE-918, which addresses Server-Side Request Forgery (SSRF) flaws where server-side code makes requests to user-supplied URLs without proper validation. In this specific implementation, the failure stems from how different components within the application stack handle URL authority parsing. While the security filter perceives a crafted input as an external domain due to its interpretation of backslash delimiters, the actual HTTP client resolves these characters in a manner that bypasses the intended boundary checks. This divergence creates a blind spot where internal IP addresses or localhost references can be masked within seemingly benign external URLs, effectively allowing the server to initiate connections to resources that should remain inaccessible from the public-facing application layer.
The operational impact of this vulnerability is severe, as it enables unauthorized access to internal network services such as database endpoints, administrative interfaces, or other microservices residing behind firewalls or security groups. An attacker with the ability to supply input URLs within the Jira or Confluence authentication flow can leverage this flaw to probe internal networks, exfiltrate sensitive data from unprotected internal APIs, or potentially pivot further into the organization's infrastructure. This aligns closely with MITRE ATT&CK technique T1598, specifically Phishing for Information Retrieval, where an attacker uses social engineering or crafted inputs to trick a system into making requests that reveal information about the network environment. The ability to bypass SSRF protections undermines the principle of least privilege and compromises the integrity of the application's security perimeter.
To mitigate this risk, organizations must immediately upgrade MCP Atlassian to version 0.22.0 or later, where the URL validation logic has been corrected to ensure consistent parsing behavior between the security checks and the HTTP client implementation. Until the update is applied, administrators should implement strict input validation at the network perimeter using Web Application Firewalls that can detect anomalous URL structures containing backslashes in authority sections. Additionally, deploying egress filtering rules to restrict outbound connections from the application server to only known external endpoints can provide a compensating control. It is also advisable to audit existing configurations for any custom integrations or plugins that might expose similar parsing vulnerabilities and ensure that all third-party tools interacting with Atlassian products adhere to strict URL sanitization standards compliant with RFC 3986.