CVE-2025-31135 Go-Guerrilla SMTP Daemon allows the PROXY command to be sent multiple times
Attackers can spoof IP addresses by sending multiple PROXY commands when ProxyOn is enabled, bypassing IP-based security controls.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-31135?
CVE-2025-31135 is a medium-severity vulnerability in phires go-guerrilla, published on 1 Apr 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-20
Which versions are affected by CVE-2025-31135?
3 open source packages ship an affected version, including github.com/phires/go-guerrilla.
| Package | Affected | Fixed in |
|---|---|---|
github.com/phires/go-guerrilla Go | All versions | 1.6.7 |
github.com/phires/go-guerrilla Go | All versions | 1.6.7 |
github.com/phires/go-guerrilla Go | All versions | 1.6.7 |
How do I fix CVE-2025-31135?
Upgrade github.com/phires/go-guerrilla to 1.6.7 or later.
Is CVE-2025-31135 being exploited?
There is no known exploitation of CVE-2025-31135 in the wild and no public exploit code.
Sources
Also known as GHSA-c2c3-pqw5-5p7c, GO-2025-3588.