CVE-2026-42261

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.

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CVSS v3.1 Score

7.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N

EPSS — Exploit Prediction

0.0008

Probability of exploitation

0.23%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-20 Improper Input Validation

CWE-693 CWE-693

CWE-918 Server-Side Request Forgery (SSRF)

Affected Products

Vendor	Product	Versions
legeling	prompthub	0.4.9 — 0.5.4

References

Advisories & Patches

https://github.com/legeling/PromptHub/releases/tag/v0.5.4 https://github.com/legeling/PromptHub/security/advisories/GHSA-9fhh-fjfg-5mr6 https://github.com/legeling/PromptHub/security/advisories/GHSA-9fhh-fjfg-5mr6

Exploits

https://github.com/legeling/PromptHub/security/advisories/GHSA-9fhh-fjfg-5mr6 https://github.com/legeling/PromptHub/security/advisories/GHSA-9fhh-fjfg-5mr6

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 7.1 (HIGH).

How severe is CVE-2026-42261? +

CVE-2026-42261 has a CVSS v3.1 score of 7.1 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0008, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-42261? +

CVE-2026-42261 affects products from legeling, specifically: prompthub. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-42261? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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