GHSA-c2c3-pqw5-5p7c
MEDIUMGo-Guerrilla SMTP Daemon allows the PROXY command to be sent multiple times
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
github.com/phires/go-guerrillaReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Summary
The PROXY command is accepted multiple times, allowing a client to spoof its IP address when the proxy protocol is being used.
Details
When ProxyOn is enabled, it looks like 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.
Note that the format of the PROXY header is well-defined. It probably shouldn't be treated as an SMTP command; parsing it the same way is likely to result in odd behavior and could lead to other vulnerabilities.
PoC
I'm working on writing a PR to fix this vulnerability. It'll include a unit test that will serve as a PoC on the current version.
Impact
Any instance with ProxyOn enabled (proxyon in the JSON config) is affected.
As far as I'm able to tell, the impact is limited to spoofing the RemoteIP field. This isn't ideal, but it probably has less practical impact on an MTA than, say, a web server.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/phires/go-guerrilla | all versions | 1.6.7 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/phires/go-guerrilla. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/phires/go-guerrilla to 1.6.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-c2c3-pqw5-5p7c is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-c2c3-pqw5-5p7c is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-c2c3-pqw5-5p7c. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-c2c3-pqw5-5p7c in your dependencies?
O3 detects GHSA-c2c3-pqw5-5p7c across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.