CVE-2026-77242: MCP Atlassian: Incomplete fix for CVE-2026-27826: DNS rebinding bypasses SSRF validation (validated IP not pinned)
MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, validateurlforssrf checks a hostname's resolved addresses, but Requests and urllib3 resolve the hostname again when connecting. A caller can use a short-lived DNS answer that is public during validation and private during connection, preserving unauthenticated access to internal or metadata endpoints despite the earlier CVE-2026-27826 remediation. The advisory traces the vulnerable input and processing flow through validateurlforssrf, checkdnsresolution, socket.getaddrinfo, and makessrfsafehook, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
MCP Atlassianto a version that resolves this vulnerability.Fixed in 0.22.0
Event History
Frequently Asked Questions
Which deployments require remediation?
MCP Atlassian versions prior to 0.22.0 are affected. The issue is fixed in version 0.22.0.
Does exploitation require authentication or user interaction?
No authentication or user interaction is required. Exploitation has high attack complexity because the attacker must cause DNS to resolve to a public address during validation and a private address when the HTTP client connects.
What could an attacker reach through a successful exploit?
A successful DNS rebinding attack can preserve access to internal or metadata endpoints despite the SSRF validation. The reported impact includes high confidentiality impact and low integrity impact.
How can teams identify potentially exposed instances?
Identify MCP Atlassian instances running a version earlier than 0.22.0 and review uses of the affected URL-processing path. The advisory identifies validate_url_for_ssrf, _check_dns_resolution, socket.getaddrinfo, and _make_ssrf_safe_hook as relevant entry points and controls.