CVE-2026-42261

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.

• CWE-20
• CWE-693
• CWE-918

• https://github.com/legeling/PromptHub/releases/tag/v0.5.4Patch, Product
• https://github.com/legeling/PromptHub/security/advisories/GHSA-9fhh-fjfg-5mr6Exploit, Mitigation, Vendor Advisory
• https://github.com/legeling/PromptHub/security/advisories/GHSA-9fhh-fjfg-5mr6Exploit, Mitigation, Vendor Advisory

Published

May 8, 2026

Last Modified

Jun 17, 2026

Status

Analyzed

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