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GHSA-jqcg-44mw-7w3h
proxy-addrImpact
proxy-addr determines which network hops are trusted proxies so that X-Forwarded-For can be believed. When an application configures a trust subnet as an IPv4-mapped IPv6 address with a short prefix, such as ::ffff:10.0.0.0/8 (the correct spelling is ::ffff:10.0.0.0/104), the subnet compiles with all-zero leading bits and matches every IPv4 address instead of the block it names. The same happens for any IPv6 trust subnet with zero leading bits, such as ::/1.
Every unauthenticated client is then trusted as a proxy at hop 0, so proxyaddr(req, trust), and therefore req.ip and req.ips in Express, returns whatever the client sends in X-Forwarded-For. This defeats IP-based access control, rate limiting, geolocation, and audit logging. The misconfiguration compiles without any error, and the same block written correctly behaves correctly, so the difference is not visible from the configuration.
Patches
Upgrade to proxy-addr 2.0.8. An IPv4 address now matches an IPv6 trust subnet only when that subnet is a genuine IPv4-mapped subnet whose prefix covers the mapped marker.
Workarounds
Write IPv4 trust subnets in plain IPv4 notation (for example 10.0.0.0/8). If IPv4-mapped IPv6 notation is required, use the full form so the prefix covers the mapped marker (for example ::ffff:10.0.0.0/104 for the 10.0.0.0/8 block).
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The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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