Vulnerability · Published May 8, 2026 · Assigned by GitHub_M
CVE-2026-42261PromptHub: Authenticated SSRF via IPv6 filter bypass in `POST /api/skills/fetch-remote`
High 7.1
In plain English
A high-severity improper input validation in PromptHub from legeling. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 15% of all known vulnerabilities).
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.
Affected products (as reported)
Weakness: CWE-20, CWE-693, CWE-918 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N
References
- https://github.com/legeling/PromptHub/security/advisories/GHSA-9fhh-fjfg-5mr6 x_refsource_CONFIRM
- https://github.com/legeling/PromptHub/releases/tag/v0.5.4 x_refsource_MISC