MCP Atlassian: Incomplete fix for GHSA-7r34-79r5-rcc9: redirect-based SSRF via unhooked requests session in Jira user-permission lookup

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=params,
    auth=auth,
    headers=headers,
    verify=self.config.ssl_verify,
)

For comparison, the equivalent non-standard-endpoint call in src/mcp_atlassian/jira/development.py correctly uses the hooked session (self.jira._session.get(...)), and the SSRF redirect hook is attached only to that session in src/mcp_atlassian/servers/dependencies.py (get_session=lambda f: f.jira._session). The bare requests.get in users.py is the one outbound path the hook does not cover.

Details — why the existing defenses do not apply here

1. self.config.url is attacker-controlled in the header-PAT branch of _get_fetcher (dependencies.py): header_config = spec.config_class(url=url_header_val, auth_type="pat", personal_token=token_header_val, ...).