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.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
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.
Which versions are affected by CVE-2026-42261?
It affects 1 product.
Products include 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.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-42261 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42261 exists.
Sources
Also known as GHSA-9fhh-fjfg-5mr6.