CVE-2026-27826

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to version 0.17.0, an unauthenticated attacker who can reach the mcp-atlassian HTTP endpoint can force the server process to make outbound HTTP requests to an arbitrary attacker-controlled URL by supplying two custom HTTP headers without an Authorization header. No authentication is required. The vulnerability exists in the HTTP middleware and dependency injection layer — not in any MCP tool handler - making it invisible to tool-level code analysis. In cloud deployments, this could enable theft of IAM role credentials via the instance metadata endpoint (169[.]254[.]169[.]254). In any HTTP deployment it enables internal network reconnaissance and injection of attacker-controlled content into LLM tool results. Version 0.17.0 fixes the issue.

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to version 0.17.0, an unauthenticated attacker who can reach the mcp-atlassian HTTP endpoint can force the server process to make outbound HTTP requests to an arbitrary attacker-controlled URL by supplying two custom HTTP headers without an Authorization header. No authentication is required. The vulnerability exists in the HTTP middleware and dependency injection layer — not in any MCP tool handler - making it invisible to tool-level code analysis. In cloud deployments, this could enable theft of IAM role credentials via the instance metadata endpoint (169[.]254[.]169[.]254). In any HTTP deployment it enables internal network reconnaissance and injection of attacker-controlled content into LLM tool results. Version 0.17.0 fixes the issue.

Summary

An unauthenticated attacker who can reach the mcp-atlassian HTTP endpoint can force the server process to make outbound HTTP requests to an arbitrary attacker-controlled URL by supplying two custom HTTP headers without an Authorization header. No authentication is required. The vulnerability exists in the HTTP middleware and dependency injection layer — not in any MCP tool handler - making it invisible to tool-level code analysis. In cloud deployments, this could enable theft of IAM role credentials via the instance metadata endpoint (169.254.169.254). In any HTTP deployment it enables internal network reconnaissance and injection of attacker-controlled content into LLM tool results.

Details

The server supports a multi-tenant HTTP authentication mode where clients supply per-request Jira/Confluence URLs via custom headers. The middleware (src/mcp_atlassian/servers/main.py:436–448) extracts X-Atlassian-Jira-Url from the request and stores it in request state with no validation. The dependency provider (src/mcp_atlassian/servers/dependencies.py:189–217) then uses this value directly as the url= parameter when constructing a JiraConfig and JiraFetcher. The first method call on the fetcher (get_current_user_account_id()) immediately issues a GET request to {header_url}/rest/api/2/myself — an outbound SSRF call to the attacker-controlled URL.

No comparison is made against the server-configured JIRA_URL environment variable. No private IP range blocklist is applied. No URL scheme allowlist is enforced.

Trigger conditions — all four must hold:

1. Server running with --transport streamable-http or --transport sse
2. Request contains X-Atlassian-Jira-Url header (any non-empty value)
3. Request contains X-Atlassian-Jira-Personal-Token header (any non-empty value)
4. Request has no Authorization header

An identical vulnerability exists for Confluence at dependencies.py:341–393 via X-Atlassian-Confluence-Url + X-Atlassian-Confluence-Personal-Token.

Root cause - middleware (src/mcp_atlassian/servers/main.py:436–448):

# When service headers are present and no Authorization header is provided,
# auth type is set to "pat" but user_atlassian_token is NOT set.
# This is what routes execution to the vulnerable path below.
if service_headers and (jira_token_str and jira_url_str):
    scope["state"]["user_atlassian_auth_type"] = "pat"

Root cause - dependency provider (src/mcp_atlassian/servers/dependencies.py:189–217):
if (
    user_auth_type == "pat"
    and jira_url_header           # attacker-controlled, no validation
    and jira_token_header
    and not hasattr(request.state, "user_atlassian_token")
):
    header_config = JiraConfig(
        url=jira_url_header,      # used directly, no allowlist check
        personal_token=jira_token_header,
        ...
    )
    header_jira_fetcher = JiraFetcher(config=header_config)
    header_jira_fetcher.get_current_user_account_id()
    # ^ GET {jira_url_header}/rest/api/2/myself — outbound SSRF call
    request.state.jira_fetcher = header_jira_fetcher  # cached for all tool calls this request


### PoC
Step 1 - Start a listener to capture the inbound SSRF request:

# listener.py
from http.server import HTTPServer, BaseHTTPRequestHandler
import json, sys

class Handler(BaseHTTPRequestHandler):
    def do_GET(self):
        print(f"[SSRF RECEIVED] Path: {self.path}", file=sys.stderr)
        print(f"[SSRF RECEIVED] Headers: {dict(self.headers)}", file=sys.stderr)
        self.send_response(200)
        self.send_header("Content-Type", "application/json")
        self.end_headers()
        if "myself" in self.path:
            self.wfile.write(json.dumps({
                "accountId": "ssrf-confirmed",
                "displayName": "SSRF PoC"
            }).encode())
        else:
           …

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to version 0.17.0, an unauthenticated attacker who can reach the mcp-atlassian HTTP endpoint can force the server process to make outbound HTTP requests to an arbitrary attacker-controlled URL by supplying two custom HTTP headers without an Authorization header. No authentication is required. The vulnerability exists in the HTTP middleware and dependency injection layer — not in any MCP tool handler - making it invisible to tool-level code analysis. In cloud deployments, this could enable theft of IAM role credentials via the instance metadata endpoint (169[.]254[.]169[.]254). In any HTTP deployment it enables internal network reconnaissance and injection of attacker-controlled content into LLM tool results. Version 0.17.0 fixes the issue.

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to version 0.17.0, an unauthenticated attacker who can reach the mcp-atlassian HTTP endpoint can force the server process to make outbound HTTP requests to an arbitrary attacker-controlled URL by supplying two custom HTTP headers without an Authorization header. No authentication is required. The vulnerability exists in the HTTP middleware and dependency injection layer — not in any MCP tool handler - making it invisible to tool-level code analysis. In cloud deployments, this could enable theft of IAM role credentials via the instance metadata endpoint (169[.]254[.]169[.]254). In any HTTP deployment it enables internal network reconnaissance and injection of attacker-controlled content into LLM tool results. Version 0.17.0 fixes the issue.

Summary

An unauthenticated attacker who can reach the mcp-atlassian HTTP endpoint can force the server process to make outbound HTTP requests to an arbitrary attacker-controlled URL by supplying two custom HTTP headers without an Authorization header. No authentication is required. The vulnerability exists in the HTTP middleware and dependency injection layer — not in any MCP tool handler - making it invisible to tool-level code analysis. In cloud deployments, this could enable theft of IAM role credentials via the instance metadata endpoint (169.254.169.254). In any HTTP deployment it enables internal network reconnaissance and injection of attacker-controlled content into LLM tool results.

Details

The server supports a multi-tenant HTTP authentication mode where clients supply per-request Jira/Confluence URLs via custom headers. The middleware (src/mcp_atlassian/servers/main.py:436–448) extracts X-Atlassian-Jira-Url from the request and stores it in request state with no validation. The dependency provider (src/mcp_atlassian/servers/dependencies.py:189–217) then uses this value directly as the url= parameter when constructing a JiraConfig and JiraFetcher. The first method call on the fetcher (get_current_user_account_id()) immediately issues a GET request to {header_url}/rest/api/2/myself — an outbound SSRF call to the attacker-controlled URL.

No comparison is made against the server-configured JIRA_URL environment variable. No private IP range blocklist is applied. No URL scheme allowlist is enforced.

Trigger conditions — all four must hold:

1. Server running with --transport streamable-http or --transport sse
2. Request contains X-Atlassian-Jira-Url header (any non-empty value)
3. Request contains X-Atlassian-Jira-Personal-Token header (any non-empty value)
4. Request has no Authorization header

An identical vulnerability exists for Confluence at dependencies.py:341–393 via X-Atlassian-Confluence-Url + X-Atlassian-Confluence-Personal-Token.

Root cause - middleware (src/mcp_atlassian/servers/main.py:436–448):

# When service headers are present and no Authorization header is provided,
# auth type is set to "pat" but user_atlassian_token is NOT set.
# This is what routes execution to the vulnerable path below.
if service_headers and (jira_token_str and jira_url_str):
    scope["state"]["user_atlassian_auth_type"] = "pat"

Root cause - dependency provider (src/mcp_atlassian/servers/dependencies.py:189–217):
if (
    user_auth_type == "pat"
    and jira_url_header           # attacker-controlled, no validation
    and jira_token_header
    and not hasattr(request.state, "user_atlassian_token")
):
    header_config = JiraConfig(
        url=jira_url_header,      # used directly, no allowlist check
        personal_token=jira_token_header,
        ...
    )
    header_jira_fetcher = JiraFetcher(config=header_config)
    header_jira_fetcher.get_current_user_account_id()
    # ^ GET {jira_url_header}/rest/api/2/myself — outbound SSRF call
    request.state.jira_fetcher = header_jira_fetcher  # cached for all tool calls this request


### PoC
Step 1 - Start a listener to capture the inbound SSRF request:

# listener.py
from http.server import HTTPServer, BaseHTTPRequestHandler
import json, sys

class Handler(BaseHTTPRequestHandler):
    def do_GET(self):
        print(f"[SSRF RECEIVED] Path: {self.path}", file=sys.stderr)
        print(f"[SSRF RECEIVED] Headers: {dict(self.headers)}", file=sys.stderr)
        self.send_response(200)
        self.send_header("Content-Type", "application/json")
        self.end_headers()
        if "myself" in self.path:
            self.wfile.write(json.dumps({
                "accountId": "ssrf-confirmed",
                "displayName": "SSRF PoC"
            }).encode())
        else:
           …

Summary

An unauthenticated attacker who can reach the mcp-atlassian HTTP endpoint can force the server process to make outbound HTTP requests to an arbitrary attacker-controlled URL by supplying two custom HTTP headers without an Authorization header. No authentication is required. The vulnerability exists in the HTTP middleware and dependency injection layer — not in any MCP tool handler - making it invisible to tool-level code analysis. In cloud deployments, this could enable theft of IAM role credentials via the instance metadata endpoint (169.254.169.254). In any HTTP deployment it enables internal network reconnaissance and injection of attacker-controlled content into LLM tool results.

Details

The server supports a multi-tenant HTTP authentication mode where clients supply per-request Jira/Confluence URLs via custom headers. The middleware (src/mcp_atlassian/servers/main.py:436–448) extracts X-Atlassian-Jira-Url from the request and stores it in request state with no validation. The dependency provider (src/mcp_atlassian/servers/dependencies.py:189–217) then uses this value directly as the url= parameter when constructing a JiraConfig and JiraFetcher. The first method call on the fetcher (get_current_user_account_id()) immediately issues a GET request to {header_url}/rest/api/2/myself — an outbound SSRF call to the attacker-controlled URL.

No comparison is made against the server-configured JIRA_URL environment variable. No private IP range blocklist is applied. No URL scheme allowlist is enforced.

Trigger conditions — all four must hold:

1. Server running with --transport streamable-http or --transport sse
2. Request contains X-Atlassian-Jira-Url header (any non-empty value)
3. Request contains X-Atlassian-Jira-Personal-Token header (any non-empty value)
4. Request has no Authorization header

An identical vulnerability exists for Confluence at dependencies.py:341–393 via X-Atlassian-Confluence-Url + X-Atlassian-Confluence-Personal-Token.

Root cause - middleware (src/mcp_atlassian/servers/main.py:436–448):

# When service headers are present and no Authorization header is provided,
# auth type is set to "pat" but user_atlassian_token is NOT set.
# This is what routes execution to the vulnerable path below.
if service_headers and (jira_token_str and jira_url_str):
    scope["state"]["user_atlassian_auth_type"] = "pat"

Root cause - dependency provider (src/mcp_atlassian/servers/dependencies.py:189–217):
if (
    user_auth_type == "pat"
    and jira_url_header           # attacker-controlled, no validation
    and jira_token_header
    and not hasattr(request.state, "user_atlassian_token")
):
    header_config = JiraConfig(
        url=jira_url_header,      # used directly, no allowlist check
        personal_token=jira_token_header,
        ...
    )
    header_jira_fetcher = JiraFetcher(config=header_config)
    header_jira_fetcher.get_current_user_account_id()
    # ^ GET {jira_url_header}/rest/api/2/myself — outbound SSRF call
    request.state.jira_fetcher = header_jira_fetcher  # cached for all tool calls this request


### PoC
Step 1 - Start a listener to capture the inbound SSRF request:

# listener.py
from http.server import HTTPServer, BaseHTTPRequestHandler
import json, sys

class Handler(BaseHTTPRequestHandler):
    def do_GET(self):
        print(f"[SSRF RECEIVED] Path: {self.path}", file=sys.stderr)
        print(f"[SSRF RECEIVED] Headers: {dict(self.headers)}", file=sys.stderr)
        self.send_response(200)
        self.send_header("Content-Type", "application/json")
        self.end_headers()
        if "myself" in self.path:
            self.wfile.write(json.dumps({
                "accountId": "ssrf-confirmed",
                "displayName": "SSRF PoC"
            }).encode())
        else:
           …