CVE-2026-77261

### Summary `_make_ssrf_safe_hook()` blocks HTTP redirects to private/internal IPs by validating the `Location` header before the client follows a `3xx` response. The problem is that this hook is only attached in one of three authentication branches — the header-PAT path. Basic auth and OAuth branches skip it entirely, so if the connected Atlassian server returns a redirect to something like `http://169.254.169.254/`, the `requests` session follows it without complaint. This is an incomplete fix for GHSA-7r34-79r5-rcc9. The hook works fine when it's there — it just isn't there for most production auth configurations. ### Details In `src/mcp_atlassian/servers/dependencies.py`, three branches construct a fetcher and call `_create_and_validate()`. Only Branch 1 passes `attach_ssrf_hook=True`: ```python # Branch 1 (header PAT) — hook attached return _create_and_validate(request, spec, header_config, "header_pat", attach_ssrf_hook=True) # Branch 2 (basic auth) — hook missing return _create_and_validate(request, spec, user_config, "basic", user_email=user_email) # Branch 3 (OAuth/PAT) — hook missing return _create_and_validate(request, spec, user_config, "oauth_pat", user_email=user_email) ``` `attach_ssrf_hook` defaults to `False`, so branches 2 and 3 silently skip the protection. The hook itself (`_make_ssrf_safe_hook`) is straightforward — it checks `response.is_redirect`, grabs the `Location` header, and calls `validate_url_for_ssrf()` to reject private IPs. It works correctly when present. Typical attack flow: 1. Attacker controls or compromises an Atlassian instance (Cloud or Server) 2. MCP server connects using basic auth or OAuth credentials (most production setups) 3. Atlassian returns `302 Location: http://169.254.169.254/latest/meta-data/iam/security-credentials/` 4. The unprotected session follows the redirect 5. AWS IAM credentials (or other internal service data) are returned to the attacker ### PoC Tested on commit `d8bc786` (v0.21.1). No real credentials needed. ```python from unittest.mock import MagicMock import requests from mcp_atlassian.servers.dependencies import _make_ssrf_safe_hook from mcp_atlassian.utils.urls import validate_url_for_ssrf from mcp_atlassian.jira import JiraFetcher from mcp_atlassian.jira.config import JiraConfig config = JiraConfig( url="https://attacker.atlassian.net", auth_type="basic", username="victim@example.com", api_token="victim-token", ) fetcher = JiraFetcher(config=config) session = fetcher.jira._session hooks = session.hooks.get("response", []) print("hooks on basic-auth session:", [h.__name__ for h in hooks] or "none") fake_redirect = MagicMock(spec=requests.Response) fake_redirect.is_redirect = True fake_redirect.headers = {"Location": "http://169.254.169.254/latest/meta-data/"} blocked = False for h in hooks: try: h(fake_redirect) except ValueError as e: blocked = True print("blocked:", e) if not blocked: print("redirect to 169.254.169.254 not blocked on basic-auth session") # show header-PAT branch does block it hook = _make_ssrf_safe_hook(validate_url_for_ssrf) try: hook(fake_redirect) except ValueError as e: print("header-PAT branch blocks:", e) ``` Output: <img width="2490" height="214" alt="image" src="https://github.com/user-attachments/assets/c7d9d7e2-4c37-4abd-95a3-4ddd9f6bd735" /> ``` $ uv run python3 /tmp/test.py hooks on basic-auth session: none redirect to 169.254.169.254 not blocked on basic-auth session header-PAT branch blocks: Redirect blocked (SSRF): Blocked IP address: 169.254.169.254 (non-global) ``` ### Impact Basic auth and OAuth cover most production Atlassian Cloud deployments, so this affects the majority of HTTP-mode multi-user setups. An attacker with control over the Atlassian server can redirect MCP server requests to internal infrastructure — cloud metadata endpoints, internal Kubernetes API, databases, or any service reachable from the MCP server's network. The fix is one line per affected branch: pass `attach_ssrf_hook=True` to `_create_and_validate()` in branches 2 and 3, the same way branch 1 already does.

### Summary `_make_ssrf_safe_hook()` blocks HTTP redirects to private/internal IPs by validating the `Location` header before the client follows a `3xx` response. The problem is that this hook is only attached in one of three authentication branches — the header-PAT path. Basic auth and OAuth branches skip it entirely, so if the connected Atlassian server returns a redirect to something like `http://169.254.169.254/`, the `requests` session follows it without complaint. This is an incomplete fix for GHSA-7r34-79r5-rcc9. The hook works fine when it's there — it just isn't there for most production auth configurations. ### Details In `src/mcp_atlassian/servers/dependencies.py`, three branches construct a fetcher and call `_create_and_validate()`. Only Branch 1 passes `attach_ssrf_hook=True`: ```python # Branch 1 (header PAT) — hook attached return _create_and_validate(request, spec, header_config, "header_pat", attach_ssrf_hook=True) # Branch 2 (basic auth) — hook missing return _create_and_validate(request, spec, user_config, "basic", user_email=user_email) # Branch 3 (OAuth/PAT) — hook missing return _create_and_validate(request, spec, user_config, "oauth_pat", user_email=user_email) ``` `attach_ssrf_hook` defaults to `False`, so branches 2 and 3 silently skip the protection. The hook itself (`_make_ssrf_safe_hook`) is straightforward — it checks `response.is_redirect`, grabs the `Location` header, and calls `validate_url_for_ssrf()` to reject private IPs. It works correctly when present. Typical attack flow: 1. Attacker controls or compromises an Atlassian instance (Cloud or Server) 2. MCP server connects using basic auth or OAuth credentials (most production setups) 3. Atlassian returns `302 Location: http://169.254.169.254/latest/meta-data/iam/security-credentials/` 4. The unprotected session follows the redirect 5. AWS IAM credentials (or other internal service data) are returned to the attacker ### PoC Tested on commit `d8bc786` (v0.21.1). No real credentials needed. ```python from unittest.mock import MagicMock import requests from mcp_atlassian.servers.dependencies import _make_ssrf_safe_hook from mcp_atlassian.utils.urls import validate_url_for_ssrf from mcp_atlassian.jira import JiraFetcher from mcp_atlassian.jira.config import JiraConfig config = JiraConfig( url="https://attacker.atlassian.net", auth_type="basic", username="victim@example.com", api_token="victim-token", ) fetcher = JiraFetcher(config=config) session = fetcher.jira._session hooks = session.hooks.get("response", []) print("hooks on basic-auth session:", [h.__name__ for h in hooks] or "none") fake_redirect = MagicMock(spec=requests.Response) fake_redirect.is_redirect = True fake_redirect.headers = {"Location": "http://169.254.169.254/latest/meta-data/"} blocked = False for h in hooks: try: h(fake_redirect) except ValueError as e: blocked = True print("blocked:", e) if not blocked: print("redirect to 169.254.169.254 not blocked on basic-auth session") # show header-PAT branch does block it hook = _make_ssrf_safe_hook(validate_url_for_ssrf) try: hook(fake_redirect) except ValueError as e: print("header-PAT branch blocks:", e) ``` Output: <img width="2490" height="214" alt="image" src="https://github.com/user-attachments/assets/c7d9d7e2-4c37-4abd-95a3-4ddd9f6bd735" /> ``` $ uv run python3 /tmp/test.py hooks on basic-auth session: none redirect to 169.254.169.254 not blocked on basic-auth session header-PAT branch blocks: Redirect blocked (SSRF): Blocked IP address: 169.254.169.254 (non-global) ``` ### Impact Basic auth and OAuth cover most production Atlassian Cloud deployments, so this affects the majority of HTTP-mode multi-user setups. An attacker with control over the Atlassian server can redirect MCP server requests to internal infrastructure — cloud metadata endpoints, internal Kubernetes API, databases, or any service reachable from the MCP server's network. The fix is one line per affected branch: pass `attach_ssrf_hook=True` to `_create_and_validate()` in branches 2 and 3, the same way branch 1 already does.