CVE-2026-48737

pyLoad: SSRF guard bypass via IPv6 6to4/NAT64 transition wrappers of internal IPs

def is_global_address(value):
    try:
        return ipaddress.ip_address(value).is_global
    except ValueError:
        return False

def is_global_host(value):
    ips = host_to_ip(value)
    return ips and all((is_global_address(ip) for ip in ips))

if not self.allow_private_ip:
    is_proxy_ip = self.http_proxy_host and self.http_proxy_host == (conn_primary_ip, conn_primary_port)
    if not is_global_address(conn_primary_ip) and not is_proxy_ip:
        return pycurl.PREREQFUNC_ABORT
return pycurl.PREREQFUNC_OK

def is_global_address(value):
    try:
        return ipaddress.ip_address(value).is_global
    except ValueError:
        return False

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

CVE-2026-48737 has a CVSS score of 4.9 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

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Treat IPv6 transition-encoding forms by unwrapping the embedded IPv4 and re-running the global check, plus an explicit blocklist of well-known embedding prefixes for defence in depth:

import ipaddress

_NAT64_WELL_KNOWN = ipaddress.IPv6Network("64:ff9b::/96")
_NAT64_DISCOVERY = ipaddress.IPv6Network("64:ff9b:1::/48")


def _embedded_ipv4(addr):
    if isinstance(addr, ipaddress.IPv6Address):
        if addr.ipv4_mapped is not None:
            return addr.ipv4_mapped
        if addr.sixtofour is not None:  # 2002::/16 6to4
            return addr.sixtofour
        if addr in _NAT64_WELL_KNOWN or addr in _NAT64_DISCOVERY:
            return ipaddress.IPv4Address(addr.packed[-4:])
    return None


def is_global_address(value):
    try:
        addr = ipaddress.ip_address(value)
    except ValueError:
        return False
    embedded = _embedded_ipv4(addr)
    if embedded is not None:
        addr = embedded
    return addr.is_global

A patch implementing this approach (plus tests covering 6to4 and NAT64 wraps for 127.0.0.1, 10.0.0.1, 172.16.0.1, 192.168.1.1, 100.64.0.0/10, and 169.254.169.254) accompanies the fix PR.

1. What is CVE-2026-48737? CVE-2026-48737 is a medium-severity server-side request forgery (SSRF) vulnerability in pyload-ng (pip), affecting versions <= 0.5.0b3.dev100. No fixed version is listed yet. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
2. How severe is CVE-2026-48737? CVE-2026-48737 has a CVSS score of 4.9 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of pyload-ng are affected by CVE-2026-48737? pyload-ng (pip) versions <= 0.5.0b3.dev100 is affected.
4. Is there a fix for CVE-2026-48737? No fixed version is listed for CVE-2026-48737 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-48737 exploitable, and should I be worried? Whether CVE-2026-48737 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-48737 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-48737? No fixed version is listed yet. In the interim: Validate and restrict destination URLs against an allowlist. Block requests to private IP ranges and cloud metadata endpoints.

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