CVE-2026-77254 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, requests to the HTTP MCP endpoint without a per-user identity are allowed to reach tool handlers, which then use globally configured Jira or Confluence credentials. A network caller can perform operations with the operator account's permissions unless the deployment has an independent authentication boundary. The advisory traces the vulnerable input and processing flow through streamable-http, UserTokenMiddleware, _get_fetcher, and global credentials, which identify the affected entry points, controls, and code paths. 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 prior to version 0.22.0 represents a critical authentication bypass within the Model Context Protocol server implementation for Atlassian products such as Confluence and Jira. The core issue stems from an insufficient validation of user identity during HTTP requests directed at the MCP endpoint. Specifically, when a network caller initiates a request without providing per-user identity information, the system fails to reject or properly handle this absence of authentication context. Instead of enforcing strict access controls that require explicit user identification, the server allows these unauthenticated or improperly authenticated requests to proceed through the processing pipeline and reach the tool handlers responsible for executing operations against Atlassian services.
This architectural flaw results in a severe authorization bypass where the system defaults to using globally configured credentials associated with an operator account rather than requiring specific user-level authentication. Consequently, any network caller capable of reaching the MCP endpoint can perform actions with the elevated permissions granted to that global operator account. This effectively neutralizes multi-tenant isolation and role-based access controls within Atlassian environments if they rely on this interface for automation or integration tasks. The impact is particularly acute in deployments where independent authentication boundaries are not established, as it allows unauthorized entities to manipulate data, modify configurations, or exfiltrate sensitive information under the guise of a privileged administrative identity.
The technical root cause lies in the handling of input and processing flows through specific components including streamable-http, UserTokenMiddleware, and _get_fetcher. The vulnerability manifests because these components do not adequately enforce the presence of valid user tokens before passing control to tool handlers that utilize global credentials. This lack of intermediate validation creates a direct path for attackers to exploit the trust relationship between the MCP server and the underlying Atlassian instances. From a threat modeling perspective, this aligns with CWE-287 Improper Authentication and CWE-862 Missing Authorization, as the system fails to verify identity and subsequently grants privileges based on default global settings rather than user-specific permissions. Furthermore, in terms of MITRE ATT&CK framework mapping, this vulnerability facilitates lateral movement and privilege escalation by allowing an attacker to leverage compromised or exposed API endpoints to act with higher-level credentials, akin to techniques observed in credential abuse scenarios where service accounts are misused for unauthorized access.
To mitigate this risk, organizations must immediately upgrade MCP Atlassian to version 0.22.0 or later, which addresses the flawed input validation logic and ensures that per-user identity is strictly required before tool handlers execute operations. For deployments unable to update instantly, implementing an independent authentication boundary at the network level or reverse proxy layer can provide a temporary control mechanism by enforcing strict access policies before requests reach the MCP endpoint. Additionally, reviewing global credential usage patterns and minimizing the scope of permissions assigned to operator accounts used in automation workflows will reduce the blast radius should such vulnerabilities be exploited in other contexts. Regular auditing of API access logs for anomalous activity involving unauthenticated or broadly authenticated requests is also recommended to detect potential exploitation attempts early.