# CVE-2026-42261: PromptHub: Authenticated SSRF via IPv6 filter bypass in `POST /api/skills/fetch-remote`

> Authenticated users can bypass IPv6 filters to perform Server-Side Request Forgery, accessing internal network resources and sensitive data.

- **Severity:** High 7.1 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 8 May 2026
- **Updated:** 11 May 2026
- **Also known as:** GHSA-9fhh-fjfg-5mr6

## What is CVE-2026-42261?

CVE-2026-42261 is a high-severity server-side request forgery vulnerability in legeling PromptHub, published on 8 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

PromptHub is an all-in-one AI toolbox for prompt, skill, and agent management. From version 0.4.9 to before version 0.5.4, apps/web/src/routes/skills.ts exposes an authenticated endpoint POST /api/skills/fetch-remote that fetches a user-supplied URL server-side and reflects the response body (up to 5 MB) back to the caller. The SSRF protection in apps/web/src/utils/remote-http.ts (isPrivateIPv6) attempts to block private/loopback destinations, but multiple alternate-but-valid IPv6 representations bypass the check. The bypasses reach any IPv4 address (loopback, RFC1918, link-local) via IPv4-mapped IPv6 in hex form, and the canonical ::1 via any representation that isn't the literal string "::1". Any authenticated user (role: user or admin) can trigger the SSRF. On deployments configured with ALLOW_REGISTRATION=true — a supported and documented configuration — this means any internet user who can register. This issue has been patched in version 0.5.4.

Weakness: CWE-918 (Server-Side Request Forgery), CWE-693 (Protection Mechanism Failure), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-42261?

It affects 1 product.


Products: Legeling Prompthub.

## How do I fix CVE-2026-42261?

No fix has been published for CVE-2026-42261 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-42261 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42261 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42261 and fix it if it is affected.

What it is: CVE-2026-42261 is a high-severity server-side request forgery vulnerability in legeling PromptHub, published on 8 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42261 exists.

Affected product: legeling PromptHub. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-42261/ (Markdown: https://insights.sbomify.com/CVE-2026-42261/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42261
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42261
- OSV: https://osv.dev/vulnerability/CVE-2026-42261

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42261/
Summaries are generated and may contain mistakes; the official description above is the record.