CVE-2026-42261: CWE-20: Improper Input Validation in legeling PromptHub
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.
AI Analysis
Technical Summary
PromptHub's authenticated POST /api/skills/fetch-remote endpoint fetches a user-supplied URL and returns the response body. The SSRF protection attempts to block private and loopback IP addresses using an IPv6 check (isPrivateIPv6), but multiple alternate valid IPv6 representations bypass this check. This allows attackers to reach internal IPv4 addresses (loopback, RFC1918, link-local) via IPv4-mapped IPv6 addresses in hex form and bypass canonical checks for ::1. The vulnerability affects versions >=0.4.9 and <0.5.4 and requires authentication, but with ALLOW_REGISTRATION=true, any internet user can register and exploit it. The vulnerability is tracked as CVE-2026-42261 with a CVSS 3.1 score of 7.1 (high severity).
Potential Impact
An attacker with authenticated access can perform server-side request forgery (SSRF) to internal network addresses, potentially accessing sensitive internal resources. The vulnerability allows reading response bodies up to 5 MB from arbitrary internal endpoints. This could lead to information disclosure and partial integrity impact. The CVSS vector indicates high confidentiality impact, low integrity impact, and no availability impact.
Mitigation Recommendations
This vulnerability has been patched in PromptHub version 0.5.4. Users should upgrade to version 0.5.4 or later to remediate this issue. No official vendor advisory content is provided here, but the patch status is confirmed by the vulnerability description. Until upgraded, restrict user registration or authenticated access to trusted users to reduce exposure.
CVE-2026-42261: CWE-20: Improper Input Validation in legeling PromptHub
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.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
PromptHub's authenticated POST /api/skills/fetch-remote endpoint fetches a user-supplied URL and returns the response body. The SSRF protection attempts to block private and loopback IP addresses using an IPv6 check (isPrivateIPv6), but multiple alternate valid IPv6 representations bypass this check. This allows attackers to reach internal IPv4 addresses (loopback, RFC1918, link-local) via IPv4-mapped IPv6 addresses in hex form and bypass canonical checks for ::1. The vulnerability affects versions >=0.4.9 and <0.5.4 and requires authentication, but with ALLOW_REGISTRATION=true, any internet user can register and exploit it. The vulnerability is tracked as CVE-2026-42261 with a CVSS 3.1 score of 7.1 (high severity).
Potential Impact
An attacker with authenticated access can perform server-side request forgery (SSRF) to internal network addresses, potentially accessing sensitive internal resources. The vulnerability allows reading response bodies up to 5 MB from arbitrary internal endpoints. This could lead to information disclosure and partial integrity impact. The CVSS vector indicates high confidentiality impact, low integrity impact, and no availability impact.
Mitigation Recommendations
This vulnerability has been patched in PromptHub version 0.5.4. Users should upgrade to version 0.5.4 or later to remediate this issue. No official vendor advisory content is provided here, but the patch status is confirmed by the vulnerability description. Until upgraded, restrict user registration or authenticated access to trusted users to reduce exposure.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-04-26T11:53:27.705Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 69fd5dbdcbff5d86108b645f
Added to database: 5/8/2026, 3:51:25 AM
Last enriched: 5/8/2026, 4:06:49 AM
Last updated: 5/9/2026, 3:48:19 AM
Views: 8
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