Go-Guerrilla SMTP Daemon allows the PROXY command to be sent multiple times
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- None · Low · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| phires | go-guerrilla | before 1.6.7 | 1.6.7 | Patch available | CNA |
| — | github.com/phires/go-guerrilla (Go) | before 1.6.7 | 1.6.7 | Patch available | GHSA-c2c3-pqw5-5p7c |
- go-guerrilla Vendorphires Affected before 1.6.7 Fixed in 1.6.7 Patch available CNA
- github.com/phires/go-guerrilla (Go) Vendor— Affected before 1.6.7 Fixed in 1.6.7 Patch available GHSA-c2c3-pqw5-5p7c
Remediation
- Fix · CNA go-guerrilla (phires) Fixed in 1.6.7
- Fix · GHSA-c2c3-pqw5-5p7c github.com/phires/go-guerrilla (Go) Fixed in 1.6.7 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2025-31135
- 2026-10-03 Alias added: GHSA-c2c3-pqw5-5p7c
References
Other 5
- https://github.com/phires/go-guerrilla/security/advisories/GHSA-c2c3-pqw5-5p7c
- https://github.com/phires/go-guerrilla/commit/d08fe22f8022d2bdedc136f9e4ba96f2fbbebf18
- https://github.com/phires/go-guerrilla/commit/7673947f2d5204a135d7ae0b7f80759e548abee6
- https://github.com/phires/go-guerrilla
- https://pkg.go.dev/vuln/GO-2025-3588
Sources
- CVE-2025-31135 · CVE Program
- CVE-2025-31135 · NVD
- FIRST EPSS
- GHSA-c2c3-pqw5-5p7c · GitHub Advisory Database · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences