# GHSA-84g5-x8j3-7235: Netfoil has incorrect allowlist enforcement

> An off-by-one error in Netfoil's suffix trie allows attackers to bypass domain allowlists by modifying the first character of a URL.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 Apr 2026
- **Also known as:** GO-2026-5240

## What is GHSA-84g5-x8j3-7235?

GHSA-84g5-x8j3-7235 is a vulnerability in github.com/tinfoil-factory/netfoil, published on 29 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

### Summary
Rules could be bypassed by changing the first character: `example.com` could be be bypassed by e.g. `fxample.com`.

### Details
Off-by-one error in the suffixtrie implementation.

### Impact
The domain filter could be bypassed. Please note that DNS filtering alone is not enough to block malicious traffic.

## Which versions are affected by GHSA-84g5-x8j3-7235?

3 open source packages ship an affected version, including github.com/tinfoil-factory/netfoil.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/tinfoil-factory/netfoil` | Go | All versions | 0.2.1 |
| `github.com/tinfoil-factory/netfoil` | Go | All versions | 0.2.1 |
| `github.com/tinfoil-factory/netfoil` | Go | All versions | 0.2.1 |

## How do I fix GHSA-84g5-x8j3-7235?

Upgrade github.com/tinfoil-factory/netfoil to 0.2.1 or later.

## Is GHSA-84g5-x8j3-7235 being exploited?

There is no known exploitation of GHSA-84g5-x8j3-7235 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-84g5-x8j3-7235 and fix it if it is affected.

What it is: GHSA-84g5-x8j3-7235 is a vulnerability in github.com/tinfoil-factory/netfoil, published on 29 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-84g5-x8j3-7235 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/tinfoil-factory/netfoil (Go): affected all versions; fixed in 0.2.1
- github.com/tinfoil-factory/netfoil (Go): affected all versions; fixed in 0.2.1
- github.com/tinfoil-factory/netfoil (Go): affected all versions; fixed in 0.2.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/GHSA-84g5-x8j3-7235/ (Markdown: https://insights.sbomify.com/GHSA-84g5-x8j3-7235/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-84g5-x8j3-7235

---
From sbomify Insights: https://insights.sbomify.com/GHSA-84g5-x8j3-7235/
Summaries are generated and may contain mistakes; the official description above is the record.