What’s Vulnerable › Vulnerabilities

CVE-2025-31135: Go-Guerrilla SMTP Daemon allows the PROXY command to be sent multiple times

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-04-01 · updated 2026-06-17
• Weakness: CWE-20

Description

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.

Affected products

• phires go-guerrilla: before 1.6.7

References

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

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