The SSRF guard in pyload-ng uses the is_global_address function to block non-globally routable IPs, relying on Python's ipaddress.ip_address(value).is_global property. However, this property incorrectly returns True for IPv6 6to4 (2002::/16) and NAT64 (64:ff9b::/96) transition prefixes, which encapsulate internal IPv4 addresses. As a result, pyload-ng's SSRF protections can be bypassed by supplying IPv6 literals or AAAA DNS records that map to internal IPv4 addresses via these transition mechanisms. This leads to potential internal network reconnaissance and limited data exfiltration, such as cloud metadata access. The vulnerability affects pyload-ng versions from the introduction of is_global_address/is_global_host up to an unspecified fixed version. Exploitation requires the host network to route 6to4 or NAT64 traffic and privileges to add links (Perms.ADD).

An attacker with limited privileges (Perms.ADD) can bypass SSRF protections in pyload-ng by exploiting the incorrect classification of IPv6 6to4 and NAT64 transition addresses as globally routable. This enables internal network reconnaissance and timing-based confirmation of internal endpoints, including potential exfiltration of cloud metadata services. The impact is limited to confidentiality and availability with no direct integrity impact. Exploitation requires specific network routing conditions (6to4 or NAT64) and is rated medium severity (CVSS 4.7).

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, users should be aware that SSRF protections relying on is_global_address may be bypassed via IPv6 transition addresses. Restricting or monitoring the use of IPv6 6to4 and NAT64 prefixes in network configurations and DNS records may reduce risk. Avoid running pyload-ng on Python versions 3.9 through 3.11 where 6to4 is classified as global. Follow vendor updates for official fixes.