CVE-2026-77274: MCP Atlassian: SSRF Protection Bypass

The 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/%5C@www.baidu.com/rest/api/2/myself

This allows an attacker-controlled Jira URL to target loopback or internal services.