CVE-2025-31135Network attack vector

Unauthenticated IP spoofing via repeated PROXY commands

Published Apr 1, 2025 · Updated Jan 28, 2026

Improper input validation in Go-Guerrilla before 1.6.7 allows remote attackers to spoof client IP addresses via repeated PROXY commands. In server.go, the SMTP command loop treats every matching PROXY line as trusted proxy metadata and overwrites client.RemoteIP instead of accepting only the connection's initial header. The server must have ProxyOn enabled; exploitation needs no authentication or user interaction, and the documented impact is limited to the recorded remote IP.

CVSS severity5.3
Medium
EPSS probability0.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Go-Guerrilla before 1.6.7 allows remote attackers to spoof client IP addresses via repeated PROXY commands. In server.go, the SMTP command loop treats every matching PROXY line as trusted proxy metadata and overwrites client.RemoteIP instead of accepting only the connection's initial header. The server must have ProxyOn enabled; exploitation needs no authentication or user interaction, and the documented impact is limited to the recorded remote IP.

The record

CVE
CVE-2025-31135
Published
Apr 1, 2025
Updated
Jan 28, 2026
Vendor
Philipp Resch
Product
Go-Guerrilla
Classifications
CWE-20, T1036
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 1, 2025CVE publishedPublication date reported by the CVE source.
  2. Jan 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.6.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Philipp Resch · Go-Guerrillaversion=< 1.6.7

Published CVSS scores

5.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T1036Masquerading

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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