CVE-2025-31135

Go-Guerrilla SMTP Daemon is a lightweight SMTP server written in Go. Prior to 1.6.7, when ProxyOn is enabled, the PROXY command will be accepted multiple times, with later invocations overriding earlier ones. The proxy protocol only supports one initial PROXY header; anything after that is considered part of the exchange between client and server, so the client is free to send further PROXY commands with whatever data it pleases. go-guerrilla will treat these as coming from the reverse proxy, allowing a client to spoof its IP address. This vulnerability is fixed in 1.6.7.

• CWE-20

• https://github.com/phires/go-guerrilla/commit/d08fe22f8022d2bdedc136f9e4ba96f2fbbebf18
• https://github.com/phires/go-guerrilla/security/advisories/GHSA-c2c3-pqw5-5p7c

Published

Apr 1, 2025

Last Modified

Jun 17, 2026

Status

Deferred

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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