| Package | Affected versions | Patched versions |
|---|---|---|
| mcp-atlassian | < 0.22.0 | 0.22.0 |
| mcp atlassian | < 0.22.0 | 0.22.0 |
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
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Preconditions: the server is running in HTTP transport (streamable-http or sse) multi-tenant mode, as described in the GHSA-7r34-79r5-rcc9 advisory (binds 0.0.0.0, per-request header auth, no server-side credentials).
The server makes an outbound GET to the internal target, confirming SSRF.
Impact
Blind, unauthenticated server-side request forgery from the mcp-atlassian host. An attacker who can reach the HTTP transport endpoint can cause the server to issue GET requests to arbitrary internal hosts and ports (internal service reachability and port discovery, triggering of internal GET-actuated endpoints, reachability of cloud metadata endpoints). The response body is not reflected to the attacker except in the narrow case where an internal service returns a JSON object shaped like {"users": [...]}, so this is primarily a blind SSRF: weaker than the original CVE-2026-27826 (no general internal data exfiltration), but the redirect-based internal-reachability that GHSA-7r34-79r5-rcc9 intended to close remains exploitable through this code path in the latest release (v0.21.1).
Suggested Remediation
Route the request through the hooked session instead of the module-level requests, mirroring development.py:
response = self.jira._session.get(
url,
params=params,
verify=self.config.ssl_verify,
)
(The session already carries the appropriate authentication, so the manual auth / Authorization handling can be dropped.) More generally, auditing for any remaining bare requests.* / httpx.* calls that use self.config.url and routing them through the SSRF-hooked session would prevent recurrence.
Coordinated Disclosure
This appears to be an incomplete fix for GHSA-7r34-79r5-rcc9 (CVE-2026-27826). If you agree, I would kindly ask you to consider requesting a CVE ID for this residual instance through this repository's Security Advisory "Request CVE ID" workflow once confirmed, so that downstream users and distributions can track the additional fix. The severity here is lower than the parent advisory — it is a blind, redirect-only SSRF gated on the HTTP multi-tenant deployment mode — so a Medium rating seems appropriate, and I defer to your judgment on the final score. Thank you very much for your time and for your work on this project.