MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, JiraUserMixin._lookup_user_by_permissions uses the module-level requests.get function instead of the fetcher's protected session. A caller-controlled public Jira URL can redirect that unhooked request to an internal address, bypassing the redirect checks added for CVE-2026-27826. The advisory traces the vulnerable input and processing flow through JiraUserMixin._lookup_user_by_permissions, requests.get, self.jira._session.get, and _make_ssrf_safe_hook, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.

Affected: PyPI: mcp-atlassian

Summary

The fix for the SSRF vulnerability tracked as GHSA-7r34-79r5-rcc9 / CVE-2026-27826 is incomplete. That fix added two defenses: validate_url_for_ssrf() on the per-request X-Atlassian-Jira-Url / X-Atlassian-Confluence-Url headers (blocking a directly-internal base URL), and a redirect-validation hook (_make_ssrf_safe_hook) attached to the fetcher's HTTP session so that an attacker-controlled public host cannot redirect outbound requests to an internal address.

However, one outbound request path does not go through the hooked session. JiraUserMixin._lookup_user_by_permissions issues its request with the module-level requests.get instead of self.jira._session.get, so the redirect-validation hook never runs for it. An unauthenticated attacker (in the HTTP / multi-tenant transport mode that binds 0.0.0.0 with no credentials) can therefore set a public base URL that passes validate_url_for_ssrf(), then have their own server return an HTTP redirect to an internal address. The bare requests.get follows that redirect with no validation, resulting in a blind server-side request to an arbitrary internal host and port.

Affected component

src/mcp_atlassian/jira/users.py, method _lookup_user_by_permissions (the requests.get(...) call):

url = f"{self.config.url}/rest/api/2/user/permission/search" params = {"query": username, "permissions": "BROWSE"} ... response = requests.get( # module-level requests, NOT self.jira._session url, params…

Affected: PyPI: mcp-atlassian

Summary

The fix for the SSRF vulnerability tracked as GHSA-7r34-79r5-rcc9 / CVE-2026-27826 is incomplete. That fix added two defenses: validate_url_for_ssrf() on the per-request X-Atlassian-Jira-Url / X-Atlassian-Confluence-Url headers (blocking a directly-internal base URL), and a redirect-validation hook (_make_ssrf_safe_hook) attached to the fetcher's HTTP session so that an attacker-controlled public host cannot redirect outbound requests to an internal address.

However, one outbound request path does not go through the hooked session. JiraUserMixin._lookup_user_by_permissions issues its request with the module-level requests.get instead of self.jira._session.get, so the redirect-validation hook never runs for it. An unauthenticated attacker (in the HTTP / multi-tenant transport mode that binds 0.0.0.0 with no credentials) can therefore set a public base URL that passes validate_url_for_ssrf(), then have their own server return an HTTP redirect to an internal address. The bare requests.get follows that redirect with no validation, resulting in a blind server-side request to an arbitrary internal host and port.

Affected component

src/mcp_atlassian/jira/users.py, method _lookup_user_by_permissions (the requests.get(...) call):

url = f"{self.config.url}/rest/api/2/user/permission/search" params = {"query": username, "permissions": "BROWSE"} ... response = requests.get( # module-level requests, NOT self.jira._session url, params…