# CVE-2026-54450: ToolHive: SSRF guard misses IPv6 NAT64 ranges (64:ff9b::/96, 64:ff9b:1::/48), allowing metadata/internal access behind a NAT64 gateway

> Attacker can bypass SSRF protections via IPv6 NAT64 addresses to probe internal network reachability on ToolHive deployments behind NAT64 gateways.

- **Severity:** Low 2.9 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Sep 2026
- **Updated:** 15 Sep 2026
- **Also known as:** GHSA-pph6-vfjv-vpjw, GO-2026-5996

## What is CVE-2026-54450?

CVE-2026-54450 is a low-severity server-side request forgery vulnerability in stacklok toolhive, published on 15 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

ToolHive is a utility designed to simplify the deployment and management of Model Context Protocol (MCP) servers. Prior to 0.29.1, networking.IsPrivateIP in pkg/networking/utilities.go omits the IPv6 NAT64 prefixes 64:ff9b::/96 and 64:ff9b:1::/48, so NAT64 addresses embedding private, loopback, or link-local IPv4 targets are classified as public and allowed. The most direct attacker-controlled path begins when an external OAuth client supplies a client_id URL that CIMDStorageDecorator.GetClient routes through FetchClientMetadataDocument in pkg/oauthproto/cimd/fetch.go; protectedDialerControl in pkg/networking/http_client.go and validateHost in pkg/skills/gitresolver/reference.go share the defective classification but use operator-controlled or user-controlled destinations. On a ToolHive host behind a NAT64/DNS64 gateway, the gateway translates an allowed address such as 64:ff9b:1::a9fe:a9fe to 169.254.169.254, permitting blind probing of internal TCP or TLS reachability. The attacker-controlled CIMD path requires HTTPS, verifies certificates, and does not reflect response bodies, so the established impact is an internal reachability oracle rather than metadata credential exfiltration; the webhook client is not affected because it does not use this IP guard. This issue is fixed in version 0.29.1.

Weakness: CWE-918 (Server-Side Request Forgery)

## Which versions are affected by CVE-2026-54450?

3 open source packages ship an affected version, including github.com/stacklok/toolhive.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/stacklok/toolhive` | Go | All versions | 0.29.1 |
| `github.com/stacklok/toolhive` | Go | All versions | 0.29.1 |
| `github.com/stacklok/toolhive` | Go | All versions | 0.29.1 |

## How do I fix CVE-2026-54450?

Upgrade github.com/stacklok/toolhive to 0.29.1 or later.

## Is CVE-2026-54450 being exploited?

There is no known exploitation of CVE-2026-54450 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54450 and fix it if it is affected.

What it is: CVE-2026-54450 is a low-severity server-side request forgery vulnerability in stacklok toolhive, published on 15 Sep 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 CVE-2026-54450 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/stacklok/toolhive (Go): affected all versions; fixed in 0.29.1
- github.com/stacklok/toolhive (Go): affected all versions; fixed in 0.29.1
- github.com/stacklok/toolhive (Go): affected all versions; fixed in 0.29.1

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/CVE-2026-54450/ (Markdown: https://insights.sbomify.com/CVE-2026-54450/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54450
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54450
- OSV: https://osv.dev/vulnerability/CVE-2026-54450

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54450/
Summaries are generated and may contain mistakes; the official description above is the record.